Optical filter and imaging apparatus

ABSTRACT

An optical (1a) includes a light-absorbing layer (10). The light-absorbing layer absorbs light in at least a portion of the near-infrared region. When light with a wavelength of 300 to 1200 nm is incident on the optical filter (1a) at an incident angle of 0°, the optical filter (1a) satisfies given spectral transmittance requirements. When an average of absolute values of differences each between a value of a normalized spectral transmittance for an incident angle x° and a value of a normalized spectral transmittance for an incident angle y° in the wavelength range of W nm to V nm (W&lt;V) is expressed as ΔTSSx/yW-V, the optical filter (1a) satisfies requirements ΔTS0/40380-530≤3%, ΔTS0/40450-650≤3%, and ΔTS0/40530-750≤3%.

TECHNICAL FIELD

The present invention relates to an optical filter and an imagingapparatus.

BACKGROUND ART

Imaging apparatuses including an optical filter such as a near-infraredcut filter are conventionally known. For example, Patent Literature 1describes a near-infrared cut filter including a laminated sheet havinga near-infrared-absorber-including resin layer provided on at least oneside of a glass sheet substrate. For example, this near-infrared cutfilter has a dielectric multilayer film provided on at least one side ofthe laminated sheet. For this near-infrared cut filter, the absolutevalue |Ya−Yb| of the difference between a wavelength value (Ya) and awavelength value (Yb) is less than 15 nm. The wavelength value (Ya) is avalue of a wavelength which lies in the wavelength range of 560 to 800nm and at which the transmittance measured in the directionperpendicular to the near-infrared cut filter is 50%. The wavelengthvalue (Yb) is a value of a wavelength which lies in the wavelength rangeof 560 to 800 nm and at which the transmittance measured at an incidentangle of 30° to the near-infrared cut filter is 50%. As just described,the dependence of the transmission characteristics of the near-infraredcut filter according to Patent Literature 1 on the incident angle oflight is adjusted to be small.

Patent Literature 2 describes a near-infrared cut filter including anear-infrared-absorbing glass substrate, near-infrared-absorbing layer,and dielectric multilayer film. The near-infrared-absorbing layerincludes a near-infrared-absorbing dye and transparent resin. PatentLiterature 2 describes a solid-state imaging apparatus including thisnear-infrared cut filter and a solid-state imaging device. According toPatent Literature 2, the influence of the incident angle dependencewhich dielectric multilayer films inherently have and which isdependence of a shift of a blocking wavelength on the incident angle oflight can be almost completely eliminated by laminating thenear-infrared-absorbing glass substrate and near-infrared-absorbinglayer. For example, in Patent Literature 2, a transmittance (T₀) at anincident angle of 0° and a transmittance (T₃₀) at an incident angle of30° are measured for the near-infrared cut filter.

Patent Literatures 3 and 4 each describe an infrared cut filterincluding a transparent dielectric substrate, an infrared-reflectinglayer, and an infrared-absorbing layer. The infrared-reflecting layer isformed of a dielectric multilayer film. The infrared-absorbing layerincludes an infrared-absorbing dye. Patent Literatures 3 and 4 eachdescribe an imaging apparatus including this infrared cut filter. PatentLiteratures 3 and 4 each describe transmittance spectra shown by theinfrared cut filter for light incident at incident angles of 0°, 25°,and 35°.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2012-103340 A

Patent Literature 2: WO 2014/030628 A1

Patent Literature 3: JP 2014-52482 A

Patent Literature 4: JP 2014-203044 A

SUMMARY OF INVENTION Technical Problem

The above patent literatures fail to specifically discuss thecharacteristics which would be exhibited by the optical filters whenlight is incident on the optical filters at an incident angle largerthan 35° (e.g., 40° or larger). Therefore, the present inventionprovides an optical filter that can block unnecessary light and thatexhibits advantageous characteristics for preventing uneven coloring ofan image generated by an imaging apparatus even when the incident angleof light is larger. The present invention also provides an imagingapparatus including this optical filter.

Solution to Problem

The present invention provides an optical filter, including

a light-absorbing layer that includes a light absorber for absorbinglight in at least a portion of the near-infrared region, wherein

when light with a wavelength of 300 to 1200 nm is incident on theoptical filter at an incident angle of 0°, the optical filter satisfiesthe following requirements (1) to (9):

(1) a spectral transmittance at a wavelength of 380 nm is 20% or less;

(2) the spectral transmittance at a wavelength of 450 nm is 75% or more;

(3) an average of the spectral transmittance in the wavelength range of500 to 600 nm is 80% or more;

(4) the spectral transmittance at a wavelength of 700 nm is 5% or less;

(5) the spectral transmittance at a wavelength of 715 nm is 3% or less;

(6) an average of the spectral transmittance in the wavelength range of700 to 800 nm is 1% or less;

(7) the maximum of the spectral transmittance in the wavelength range of750 to 1080 nm is 1% or less;

(8) the maximum of the spectral transmittance in the wavelength range of1000 to 1100 nm is 2% or less; and

(9) a wavelength bandwidth of a wavelength band in which the spectraltransmittance in the wavelength range of 400 to 700 nm is 75% or more is170 nm or more, and

when light with a wavelength of 300 to 1200 nm is incident on theoptical filter at incident angles of x° and y° (0≤x≤30, 30≤y≤65, andx<y) and an average of absolute values of differences each between avalue of a normalized spectral transmittance for the incident angle x°and a value of a normalized spectral transmittance for the incidentangle y° at the same wavelength in the wavelength range of W nm to V nm(W<V) is expressed as ΔT_(S) ^(x/y) _(W-V),

the optical filter satisfies requirements ΔT_(S) ^(0/40) ₃₈₀₋₅₃₀≤3%,ΔT_(S) ^(0/40) ₄₅₀₋₆₅₀≤3%, and ΔT_(S) ^(0/40) ₅₃₀₋₇₅₀≤3%,

the normalized spectral transmittance being determined by normalizationof a spectral transmittance for each of the incident angles so that themaximum of the spectral transmittance for each of the incident angles inthe wavelength range of 400 to 650 nm is 100%.

The present invention also provides an imaging apparatus including:

a lens system;

an imaging device that receives light having been transmitted throughthe lens system; and

the above optical filter that is disposed ahead of the imaging device.

Advantageous Effects of Invention

The above optical filter can block unnecessary light and exhibitsadvantageous characteristics for preventing uneven coloring of an imagegenerated by an imaging apparatus even when the incident angle of lightis larger. Moreover, an image generated by the above imaging apparatusof the present invention is unlikely to be colored unevenly.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a cross-sectional view of an example of an optical filter ofthe present invention.

FIG. 1B is a cross-sectional view of another example of the opticalfilter of the present invention.

FIG. 1C is a cross-sectional view of yet another example of the opticalfilter of the present invention.

FIG. 1D is a cross-sectional view of yet another example of the opticalfilter of the present invention.

FIG. 1E is a cross-sectional view of yet another example of the opticalfilter of the present invention.

FIG. 2 is a cross-sectional view showing an example of an imagingapparatus according to the present invention.

FIG. 3A shows transmittance spectra shown by an optical filter accordingto Example 1 for light incident at incident angles of 0°, 3°, 35°, and40°.

FIG. 3B shows transmittance spectra shown by the optical filteraccording to Example 1 for light incident at incident angles of 45°,50°, 55°, 60°, and 65°.

FIG. 4A shows normalized transmittance spectra shown by the opticalfilter according to Example 1 for light incident at incident angles of0°, 30°, 35°, and 40°.

FIG. 4B shows normalized transmittance spectra shown by the opticalfilter according to Example 1 for light incident at incident angles of45°, 50°, 55°, 60°, and 65°.

FIG. 5A shows transmittance spectra shown by an optical filter accordingto Example 2 for light incident at incident angles of 0°, 30°, 35°, and40°.

FIG. 5B shows transmittance spectra shown by the optical filteraccording to Example 2 for light incident at incident angles of 45°,50°, 55°, 60°, and 65°.

FIG. 6A shows normalized transmittance spectra shown by the opticalfilter according to Example 2 for light incident at incident angles of0°, 30°, 35°, and 40°.

FIG. 6B shows normalized transmittance spectra shown by the opticalfilter according to Example 2 for light incident at incident angles of45°, 50°, 55°, 60°, and 65°.

FIG. 7A shows transmittance spectra shown by an optical filter accordingto Example 3 for light incident at incident angles of 0°, 30°, 35°, and40°.

FIG. 7B shows transmittance spectra shown by the optical filteraccording to Example 3 for light incident at incident angles of 45°,50°, 55°, 60°, and 65°.

FIG. 8A shows normalized transmittance spectra shown by the opticalfilter according to Example 3 for light incident at incident angles of0°, 30°, 35°, and 40°.

FIG. 8B shows normalized transmittance spectra shown by the opticalfilter according to Example 3 for light incident at incident angles of45°, 50°, 55°, 60°, and 65°.

FIG. 9A shows a transmittance spectrum shown by an intermediate productof an optical filter according to Example 4 for light incident at anincident angle of 0°.

FIG. 9B shows a transmittance spectrum shown by another intermediateproduct of the optical filter according to Example 4 for light incidentat an incident angle of 0°.

FIG. 9C shows a transmittance spectrum shown by a laminate according to

Reference Example 1 for light incident at an incident angle of 0°.

FIG. 9D shows transmittance spectra shown by a laminate according toReference Example 2 for light incident at incident angles of 0°,30°,50°, and 65°.

FIG. 10A shows transmittance spectra shown by the optical filteraccording to Example 4 for light incident at incident angles of 0°, 3°,35°, and 40°.

FIG. 10B shows transmittance spectra shown by the optical filteraccording to Example 4 for light incident at incident angles of 45°,50°, 5°, 60°, and 65°.

FIG. 11A shows normalized transmittance spectra shown by the opticalfilter according to Example 4 for light incident at incident angles of0°, 30°, 35°, and 40°.

FIG. 11B shows normalized transmittance spectra shown by the opticalfilter according to Example 4 for light incident at incident angles of45°, 50°, 55°, 60°, and 65°.

FIG. 12A shows transmittance spectra shown by an intermediate product ofan optical filter according to Comparative Example 1 for light incidentat incident angles of 0°, 30°, and 50°.

FIG. 12B shows a transmittance spectrum shown by a laminate according toReference Example 3 for light incident at an incident angle of 0°.

FIG. 13A shows transmittance spectra shown by the optical filteraccording to Comparative Example 1 for light incident at incident anglesof 0°, 30°, 35°, and 40°.

FIG. 13B shows transmittance spectra shown by the optical filteraccording to Comparative Example 1 for light incident at incident anglesof 45°, 50°, 55°, 60°, and 65°.

FIG. 14A shows normalized transmittance spectra shown by the opticalfilter according to Comparative Example 1 for light incident at incidentangles of 0°, 30°, 35°, and 40°.

FIG. 14B shows normalized transmittance spectra shown by the opticalfilter according to Comparative Example 1 for light incident at incidentangles of 45°, 50°, 55°, 60°, and 65°.

FIG. 15A shows a transmittance spectrum shown by a light-absorbingtransparent substrate used for fabrication of an optical filteraccording to Comparative Example 2 for light incident at an incidentangle of 0°.

FIG. 15B shows transmittance spectra shown by a laminate according toReference Example 4 for light incident at incident angles of 0°, 30°,and 50°.

FIG. 15C shows a transmittance spectrum shown by a laminate according toReference Example 5 for light incident at an incident angle of 0°.

FIG. 16A shows transmittance spectra shown by the optical filteraccording to Comparative Example 2 for light incident at incident anglesof 0°, 30°, 35°, and 40°.

FIG. 16B shows transmittance spectra shown by the optical filteraccording to Comparative Example 2 for light incident at incident anglesof 45°, 50°, 55°, 60°, and 65°.

FIG. 17A shows normalized transmittance spectra shown by the opticalfilter according to Comparative Example 2 for light incident at incidentangles of 0°, 30°, 35°, and 40°.

FIG. 17B shows normalized transmittance spectra shown by the opticalfilter according to Comparative Example 2 for light incident at incidentangles of 45°, 50°, 55°, 60°, and 65°.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the drawings. The following description is directed to someexamples of the present invention, and the present invention is notlimited by these examples.

The present inventors have invented the optical filter according to thepresent invention based on new findings obtained from the followingstudies of optical filters.

An optical filter blocking against unnecessary light other than visiblelight is disposed in a camera module or imaging apparatus mounted in apersonal digital assistant such as a smartphone. The use of an opticalfilter including a light-absorbing layer has been discussed to blockunnecessary light. Like the optical filters described in PatentLiteratures 1 to 4, many optical filters including a light-absorbinglayer further include a light-reflecting layer composed of a dielectricmultilayer film.

Interference of light reflecting on the front and back surfaces of eachlayer of a light-reflecting layer composed of a dielectric multilayerfilm determines a wavelength band of transmitted light and a wavelengthband of reflected light. Light can be incident on the optical filter atvarious incident angles. As the incident angle of light gets larger, theoptical path length in each layer of the light-reflecting layer changes.As a result, a phenomenon is observed in which the wavelength band oftransmitted light and the wavelength band of reflected light shift tothe short wavelength side. Therefore, it is conceivable that when lightin a given wavelength band is reflected by the light-reflecting layerthat is a dielectric multilayer film, a boundary between a wavelengthband of light to be blocked and a wavelength band of light to betransmitted is determined by a wavelength band of light absorption sothat the transmittance characteristics of the optical filter do notgreatly vary depending on the incident angle of light.

In Patent Literatures 1 and 2, the light transmission characteristics ofthe near-infrared cut filters for light incident at incident angles of0° and 30° are evaluated. In Patent Literatures 3 and 4, transmittancespectra shown by the infrared cut filters for light incident at incidentangles of 0°, 25°, and 35° are evaluated. In recent years, cameramodules and imaging apparatuses mounted in personal digital assistantssuch as smartphones have been expected to achieve a wider angle of viewand a much lower profile. Therefore, it is desirable that lighttransmission characteristics of optical filters be unlikely to vary evenwhen the incident angle of light is larger (e.g., 40° or larger).

In these points of view, for example, it is conceivable that an opticalfilter is designed so that a dielectric multilayer film will have aboundary between a wavelength band of transmitted light and a wavelengthband of reflected light at a wavelength sufficiently longer than awavelength at which a light-absorbing layer has a boundary between awavelength band of transmitted light and a wavelength band of absorbedlight. In this case, the boundary between the wavelength band of lightto be transmitted through the optical filter and a wavelength band oflight to be blocked by the optical filter is prevented from shifting tothe short wavelength side even when the incident angle of light islarger. However, when the incident angle of light is much larger, theamount of change in optical path length in each layer of thelight-reflecting layer increases and, depending on the incident angle oflight, a defect called a ripple, which is a local increase in lightreflectance and a local decrease in transmittance, can happen in awavelength band of light to be transmitted. In particular, even anoptical filter designed to be free of ripples at incident angles of 0°to 35° may suffer a ripple at an incident angle of 40° or larger.Occurrence of a ripple greatly decreases the sensitivity of an imagingapparatus to light with a certain wavelength to lower than thesensitivity thereof to light with other wavelengths and may cause unevencoloring of an image obtained therewith.

Under these circumstances, the present inventors went through much trialand error to develop an optical filter that can block unnecessary lightand that is advantageous for preventing uneven coloring of an imagegenerated by an imaging apparatus even when the incident angle of lightis larger. As a result, the present inventors have found that desirablecharacteristics can be imparted to an optical filter by a given lightabsorbing layer without combined use of a light-reflecting layercomposed of a dielectric multilayer, and thus invented the opticalfilter according to the present invention.

Herein, the term “spectral transmittance” refers to a transmittanceobtained when light with a given wavelength is incident on an objectsuch as a specimen and the term “average transmittance” refers to anaverage of the spectral transmittance in a given wavelength range.Additionally, the term “transmittance spectrum” herein refers to one inwhich spectral transmittance values at wavelengths in a given wavelengthrange are arranged in the wavelength order.

As shown in FIG. 1A, the optical filter 1 a includes a light-absorbinglayer 10. The light-absorbing layer 10 includes a light absorber. Thelight absorber absorbs light in at least a portion of the near-infraredregion. When light with a wavelength of 300 to 1200 nm is incident onthe optical filter 1 a at an incident angle of 0°, the optical filter 1a satisfies the following requirements (1) to (9):

(1) a spectral transmittance at a wavelength of 380 nm is 20% or less;

(2) the spectral transmittance at a wavelength of 450 nm is 75% or more;

(3) an average of the spectral transmittance in the wavelength range of500 to 600 nm is 80% or more;

(4) the spectral transmittance at a wavelength of 700 nm is 5% or less;

(5) the spectral transmittance at a wavelength of 715 nm is 3% or less;

(6) an average of the spectral transmittance in the wavelength range of700 to 800 nm is 1% or less;

(7) the maximum of the spectral transmittance in the wavelength range of750 to 1080 nm is 1% or less;

(8) the maximum of the spectral transmittance in the wavelength range of1000 to 1100 nm is 2% or less; and

(9) a wavelength bandwidth of a wavelength band in which the spectraltransmittance in the wavelength range of 400 to 700 nm is 75% or more is170 nm or more.

As to the above requirement (9), when a plurality of discrete wavelengthbands in which the spectral transmittance is 75% or more exists in thewavelength range of 400 to 700 nm, the sum of the wavelength bandwidthsof the plurality of wavelength bands is defined as “wavelengthbandwidth”.

When light with a wavelength of 300 to 1200 nm is incident on theoptical filter 1 a at incident angles of x° and y° (0≤x≤30, 30≤y≤65, andx<y), an average of absolute values of differences each between a valueof a normalized spectral transmittance for the incident angle x° and avalue of a normalized spectral transmittance for the incident angle y°at the same wavelength in the wavelength range of W nm to V nm (W<V) isexpressed as ΔT_(S) ^(x/y) _(W-V). In this case, the optical filter 1 asatisfies requirements ΔT_(S) ^(0/40) ₃₈₀₋₅₃₀≤3%, ΔT_(S) ^(0/40)₄₅₀₋₆₅₀≤3%, and ΔT_(S) ^(0/40) ₅₃₀₋₇₅₀≤3%.

The normalized spectral transmittance mentioned above is determined bynormalization of a spectral transmittance for each of the incidentangles so that the maximum of the spectral transmittance for each of theincident angles in the wavelength range of 400 to 650 nm will be 100%.Typically, light with a wavelength of 300 to 1200 nm is allowed to beincident on the optical filter 1 a at incident angles of 0°, 30°, 35°,40°, 45°, 50°, 55°, 60°, and 65°, and the spectral transmittance ismeasured at every 1 nm in the wavelength range of 300 to 1200 nm. Forthe spectral transmittance thus measured at each incident angle, thespectral transmittance value at each wavelength is divided by themaximum of the spectral transmittance in the wavelength range of 400 to650 nm, and the resultant value is expressed in percentage. A normalizedspectral transmittance is thus determined.

Since the optical filter 1 a has the above characteristics, the opticalfilter la can appropriately block unnecessary light such as light in thenear-infrared region without a light-reflecting layer composed of adielectric multilayer film. The optical filter 1 a may appropriatelyblock light in the ultraviolet region as well. Because of the absence ofa light-reflecting layer composed of a dielectric multilayer film fromthe optical filter 1 a, no ripple occurs in a wavelength band of lightto be transmitted even when the incident angle of light is large, and animage generated by an imaging apparatus including the optical filter 1 ais unlikely to be colored unevenly. Additionally, for the optical filter1 a, the boundary between a wavelength band of transmitted light and awavelength band of blocked light is prevented from shifting to the shortwavelength side with increase in incident angle of light. Since theoptical filter 1 a satisfies the requirements ΔT_(S) ^(0/40) ₃₈₀₋₅₃₀≤3%,ΔT_(S) ^(0/40) ₄₅₀₋₆₅₀≤3%, and ΔT_(S) ^(0/40) ₅₃₀₋₇₅₀≤3%, a gap betweenthe shape of a normalized spectral transmittance curve for an incidentangle of 0° and the shape of a normalized spectral transmittance curvefor an incident angle of 40° is small in the wavelength ranges of 380 to530 nm, 450 to 650 nm, and 530 to 750 nm.

It is conceivable that the optical filter 1 a is used, for example, whena color filter (hereinafter referred to as “RGB color filter”)consisting of R (red), G (green), and B (blue) segments is disposed ateach pixel of an imaging device such as a charge-coupled device (CCD) orcomplementary metal oxide semiconductor (CMOS). In this case, outputfrom each pixel of the imaging device is appropriately adjusted by theoptical filter 1 a, and spectral sensitivity characteristicscorresponding to the output from each pixel of the imaging device arelikely to well conform to the visual sensitivity.

An optical filter that blocks unnecessary light is commonly disposedwith its principal surface parallel to a light receiving surface of animaging device near the optical filter. In this case, light incident onthe optical filter and then on the imaging device is incident on theoptical filter and the imaging device at a substantially equal incidentangle. A chief ray is incident near the center of an imaging device atan incident angle of nearly 0° while a chief ray incident on theperipheral portion of the imaging device at a large incident angle.Therefore, in the case where the shape of a spectral sensitivity curvechanges depending on the incident angle of light incident on an imagingapparatus, the central portion and the peripheral portion of an imagetaken with the imaging apparatus differ in color when the image isdisplayed or printed. Therefore, an object expected to be colored withone color in the image is likely to gradually discolor from the centralportion toward the peripheral portion, and the discoloration is likelyto be recognized as color unevenness. Additionally, in the case wherethe shape of the spectral sensitivity curve changes in a narrow incidentangle range, e.g., 5° to 10°, discoloration is likely to occur in anarrow area on the resultant image and is particularly likely to berecognized as color unevenness. If an incident angle-dependent change inthe shape of a normalized spectral transmittance curve can be reduced bymeans of the optical filter, the incident angle-dependent change in theshape of the spectral sensitivity curve can be reduced and unevencoloring of an image generated by the imaging apparatus can beprevented.

The optical filter 1 a desirably further satisfies a requirement ΔT_(S)^(0/40) ₆₅₀₋₁₂₀₀≤1%. In this case, the gap between the shape of thenormalized spectral transmittance curve for an incident angle of 0° andthe shape of a normalized spectral transmittance curve for an incidentangle of 40° is small also in the wavelength range of 650 to 1200 nm.

The optical filter 1 a desirably further satisfies a requirement ΔT_(S)^(0/40) ₃₈₀₋₁₂₀₀≤1.5%. In this case, the gap between the shape of thenormalized spectral transmittance curve for an incident angle of 0° andthe shape of a normalized spectral transmittance curve for an incidentangle of 40° is small over the wavelength range of 380 to 1200 nm.

The wavelength range of 380 to 530 nm corresponds to the wavelengthrange referred to to determine sensitivity characteristics of asub-pixel corresponding to a B (blue) filter segment of an RGB colorfilter incorporated in or disposed near an imaging device. Thewavelength range of 450 to 650 nm corresponds to the wavelength rangereferred to to determine sensitivity characteristics of a sub-pixelcorresponding to a G (green) filter segment of an RGB color filterincorporated in or disposed near an imaging device. The wavelength rangeof 530 to 750 nm corresponds to the wavelength range referred to todetermine sensitivity characteristics of a sub-pixel corresponding to anR (red) filter segment of an RGB color filter incorporated in ordisposed near an imaging device.

The wavelength range of 650 to 1200 nm corresponds to the wavelengthrange of near-infrared light to be blocked. The wavelength range of 380to 1200 nm includes the above wavelength ranges and corresponds to thewavelength range referred to to determine the brightness of light that acamera module or an imaging apparatus takes in through the opticalfilter.

The optical filter 1 a desirably further satisfies requirements ΔT_(S)^(0/50) ₃₈₀₋₅₃₀≤4%, ΔT_(S) ^(0/50) ₄₅₀₋₆₅₀≤4%, ΔT_(S) ^(0/50)₅₃₀₋₇₅₀≤4%, ΔT_(S) ^(0/50) ₆₅₀₋₁₂₀₀≤1.5%, and ΔT_(S) ^(0/50)₃₈₀₋₁₂₀₀≤2%. In this case, a gap between the shape of the normalizedspectral transmittance curve for an incident angle of 0° and the shapeof a normalized spectral transmittance curve for an incident angle of50° is small. This makes it easy to prevent uneven coloring of an imagegenerated by an imaging apparatus even when light is incident on theoptical filter 1 a included in the imaging apparatus at an incidentangle of 50° .

The optical filter 1 a desirably further satisfies requirements ΔT_(S)^(0/60) ₃₈₀₋₅₃₀≤4.5%, ΔT_(S) ^(0/60) ₄₅₀₋₆₅₀≤4.5%, ΔT_(S) ^(0/60)₅₃₀₋₇₅₀≤4.5%, ΔT_(S) ^(0/60) ₆₅₀₋₁₂₀₀≤1.5%, and ΔT_(S) ^(0/60)₃₈₀₋₁₂₀₀≤2.5%. In this case, a gap between the shape of the normalizedspectral transmittance curve for an incident angle of 0° and the shapeof a normalized spectral transmittance curve for an incident angle of60° is small. This makes it easy to prevent uneven coloring of an imagegenerated by an imaging apparatus even when light is incident on theoptical filter 1 a included in the imaging apparatus at an incidentangle of 60°.

The optical filter 1 a desirably further satisfies requirements ΔT_(S)^(0/65) ₃₈₀₋₅₃₀≤5%, ΔT_(S) ^(0/65) ₄₅₀₋₆₅₀≤5%, ΔT_(S) ^(0/65)₅₃₀₋₇₅₀≤5%, ΔT_(S) ^(0/65) ₆₅₀₋₁₂₀₀≤1.5%, and ΔT_(S) ^(0/65)₃₈₀₋₁₂₀₀≤3%. In this case, a gap between the shape of the normalizedspectral transmittance curve for an incident angle of 0° and the shapeof a normalized spectral transmittance curve for an incident angle of65° is small. This makes it easy to prevent uneven coloring of an imagegenerated by an imaging apparatus even when light is incident on theoptical filter 1 a included in the imaging apparatus at an incidentangle of 65°. For example, when an imaging apparatus capable of takingimages using a wide-angle lens having a wide angle of view includes theoptical filter 1 a, it is easy to prevent uneven coloring of an imagetaken using the wide-angle lens.

In the case where a wide-angle lens is used in an imaging apparatus, theincident angle of light incident on a light receiving surface of animaging device can be reduced by certain design of the lens. It isinevitable, however, that light incident on a cover glass located aheadof the lens of the imaging apparatus includes light incident at a largeincident angle. When the optical filter 1 a satisfies the aboverequirements, an image generated by an imaging apparatus including theoptical filter 1 a as a cover glass is unlikely to be colored unevenly.Additionally, the optical filter 1 a functioning also as a cover glasscan reduce the number of components of the imaging apparatus and makesit easy to achieve a lower-profile imaging apparatus. Besides, in thatcase, the freedom of lens design is expanded. Moreover, flare and ghostcaused by reflection on a principal surface of a conventional opticalfilter disposed independently of a cover glass can be prevented.

The optical filter 1 a desirably further satisfies requirements ΔT_(S)^(30/40) ₃₈₀₋₅₃₀≤3%, ΔT_(S) ^(30/40) ₄₅₀₋₆₅₀≤3%, ΔT_(S) ^(30/40)₅₃₀₋₇₅₀≤3%, ΔT_(S) ^(30/40) ₆₅₀₋₁₂₀₀≤1%, and ΔT_(S) ^(30/40)₃₈₀₋₁₂₀₀≤1.5%. In this case, a gap between the shape of the normalizedspectral transmittance curve for an incident angle of 30° and the shapeof the normalized spectral transmittance curve for an incident angle of40° is small.

The optical filter 1 a desirably further satisfies requirements ΔT_(S)^(30/50) ₃₈₀₋₅₃₀≤3%, ΔT_(S) ^(30/50) ₄₅₀₋₆₅₀≤3%, ΔT_(S) ^(30/50)₅₃₀₋₇₅₀≤3%, ΔT_(S) ^(30/50) ₆₅₀₋₁₂₀₀≤1%, and ΔT_(S) ^(30/50)₃₈₀₋₁₂₀₀≤1.5%. In this case, a gap between the shape of the normalizedspectral transmittance curve for an incident angle of 30° and the shapeof the normalized spectral transmittance curve for an incident angle of50° is small.

The optical filter 1 a desirably further satisfies requirements ΔT_(S)^(30/60) ₃₈₀₋₅₃₀≤4%, ΔT_(S) ^(30/60) ₄₅₀₋₆₅₀≤4%, ΔT_(S) ^(30/60)₅₃₀₋₇₅₀≤4%, ΔT_(S) ^(30/60) ₆₅₀₋₁₂₀₀≤1.5%, and ΔT_(S) ^(30/60)₃₈₀₋₁₂₀₀≤2%. In this case, a gap between the shape of the normalizedspectral transmittance curve for an incident angle of 30° and the shapeof the normalized spectral transmittance curve for an incident angle of60° is small.

The optical filter 1 a desirably further satisfies requirements ΔT_(S)^(30/65) ₃₈₀₋₅₃₀≤4.5%, ΔT_(S) ^(30/65) ₄₅₀₋₆₅₀≤4.5%, ΔT_(S) ^(30/65)₅₃₀₋₇₅₀≤4.5%, ΔT_(S) ^(30/65) ₆₅₀₋₁₂₀₀≤1.5%, and ΔT_(S) ^(30/65)₃₈₀₋₁₂₀₀≤2.5%. In this case, a gap between the shape of the normalizedspectral transmittance curve for an incident angle of 30° and the shapeof the normalized spectral transmittance curve for an incident angle of65° is small.

When the incident angle x° of light is 0°, values of ΔT_(S) ^(0/y)_(W-V) v of the optical filter 1 a desirably satisfy the requirementsshown in Table 1.

TABLE 1 ΔTs^(0/y)W-V y = 30° y = 35° y = 40° y = 45° y = 50° y = 55° y =60° y = 65° W = 380 nm; V = 530 nm   ≤3%   ≤3%   ≤3% ≤4%   ≤4% ≤4.5%≤4.5%   ≤5% W = 450 nm; V = 650 nm   ≤3%   ≤3%   ≤3% ≤4%   ≤4% ≤4.5%≤4.5%   ≤5% W = 530 nm; V = 750 nm   <3%   ≤3%   ≤3% ≤4%   ≤4% ≤4.5%≤4.5%   ≤5% W = 650 nm; V = 1200 nm   ≤1%   ≤1%   ≤1% ≤1% ≤1.5% ≤1.5%≤1.5% ≤1.5% W = 380 nm; V = 1200 nm ≤1.5% ≤1.5% ≤1.5% ≤2%   ≤2% ≤2.5%≤2.5%   ≤3%

When the incident angle x° of light is 30°, values of ΔT_(S) ^(30/y)_(W-V) of the optical filter 1 a desirably satisfy the requirementsshown in Table 2.

TABLE 2 ΔTs^(30/y)W-V y = 35° y = 40° y = 45° y = 50° y = 55° y = 60° y= 65° W = 380 nm; V = 530 nm   ≤3%   ≤3%   ≤3%   ≤3% ≤4%   ≤4% ≤4.5% W =450 nm; V = 650 nm   ≤3%   ≤3%   ≤3%   ≤3% ≤4%   ≤4% ≤4.5% W = 530 nm; V= 750 nm   <3%   ≤3%   ≤3%   ≤3% ≤4%   ≤4% ≤4.5% W = 650 nm; V = 1200 nm  ≤1%   ≤1%   ≤1%   ≤1% ≤1% ≤1.5% ≤1.5% W = 380 nm; V = 1200 nm ≤1.5%≤1.5% ≤1.5% ≤1.5% ≤2%   ≤2% ≤2.5%

The light absorber included in the light-absorbing layer 10 is notparticularly limited as long as the light absorber absorbs light in atleast a portion of the near-infrared region and the optical filter 1 asatisfies the above requirements (1) to (9) and the requirements ΔT_(S)^(0/40) ₃₈₀₋₅₃₀≤3%, ΔT_(S) ^(0/40) ₄₅₀₋₆₅₀≤3%, and ΔT_(S) ^(0/40)₅₃₀₋₇₅₀≤3%. The light absorber is, for example, formed by a phosphonicacid and copper ion. In this case, light in a wide wavelength bandcovering the near-infrared region and a portion of the visible regionadjacent to the near-infrared region can be absorbed by thelight-absorbing layer 10. Therefore, the desired characteristics can beexhibited even when the optical filter 1 a does not include alight-reflecting layer.

When the light-absorbing layer 10 includes the light absorber formed bya phosphonic acid and copper ion, the phosphonic acid includes, forexample, a first phosphonic acid having an aryl group. In the firstphosphonic acid, the aryl group is bonded to a phosphorus atom. Thus,the above requirements are easily satisfied by the optical filter 1 a.

The aryl group of the first phosphonic acid is, for example, a phenylgroup, benzyl group, toluyl group, nitrophenyl group, hydroxyphenylgroup, halogenated phenyl group in which at least one hydrogen atom of aphenyl group is substituted by a halogen atom, or halogenated benzylgroup in which at least one hydrogen atom of a benzene ring of a benzylgroup is substituted by a halogen atom.

When the light-absorbing layer 10 includes the light absorber formed bythe phosphonic acid and copper ion, the phosphonic acid desirablyfurther includes a second phosphonic acid having an alkyl group. In thesecond phosphonic acid, the alkyl group is bonded to a phosphorus atom.

The alkyl group of the second phosphonic acid is, for example, an alkylgroup having 6 or less carbon atoms. This alkyl group may be linear orbranched.

When the light-absorbing layer 10 includes the light absorber formed bythe phosphonic acid and copper ion, the light-absorbing layer 10 furtherincludes, for example, a phosphoric acid ester allowing the lightabsorber to be dispersed and matrix resin. The light-absorbing layer 10further includes, if necessary, a hydrolytic polycondensation product ofan alkoxysilane monomer.

The phosphoric acid ester included in the light-absorbing layer 10 isnot limited to any particular one, as long as the phosphoric acid esterallows good dispersion of the light absorber. For example, thephosphoric acid ester includes at least one of a phosphoric acid diesterrepresented by the following formula (c1) and a phosphoric acidmonoester represented by the following formula (c2). In the formulae(c1) and (c2), R₂₁, R₂₂, and R₃ are each a monovalent functional grouprepresented by —(CH₂CH₂O)_(n)R₄, wherein n is an integer of 1 to 25 andR₄ is an alkyl group having 6 to 25 carbon atoms. R₂₁, R₂₂, and R₃ maybe the same or different functional groups.

The phosphoric acid ester is not particularly limited. The phosphoricacid ester can be, for example, PLYSURF A208N (polyoxyethylene alkyl(C12, C13) ether phosphoric acid ester), PLYSURF A208F (polyoxyethylenealkyl (C8) ether phosphoric acid ester), PLYSURF A208B (polyoxyethylenelauryl ether phosphoric acid ester), PLYSURF A219B (polyoxyethylenelauryl ether phosphoric acid ester), PLYSURF AL (polyoxyethylenestyrenated phenylether phosphoric acid ester), PLYSURF A212C(polyoxyethylene tridecyl ether phosphoric acid ester), or PLYSURF A215C(polyoxyethylene tridecyl ether phosphoric acid ester). All of these areproducts manufactured by DKS Co., Ltd. The phosphoric acid ester can beNIKKOL DDP-2 (polyoxyethylene alkyl ether phosphoric acid ester), NIKKOLDDP-4 (polyoxyethylene alkyl ether phosphoric acid ester), or NIKKOLDDP-6 (polyoxyethylene alkyl ether phosphoric acid ester). All of theseare products manufactured by Nikko Chemicals Co., Ltd.

The matrix resin included in the light-absorbing layer 10 is, forexample, a heat-curable or ultraviolet-curable resin in which the lightabsorber is dispersible. Additionally, as the matrix resin can be used aresin that has a transmittance of, for example, 80% or more, preferably85% or more, and more preferably 90% or more for light with a wavelengthof 350 nm to 900 nm in the form of a 0.1-mm-thick resin layer. Thematrix resin is not limited to a particular resin as long as the opticalfilter 1 a satisfies the above requirements (1) to (9) and therequirements ΔT_(S) ^(0/40) ₃₈₀₋₅₃₀≤3%, ΔT_(S) ^(0/40) ₄₅₀₋₆₅₀≤3%, andΔT_(S) ^(0/40) ₅₃₀₋₇₅₀≤3%. The content of the phosphonic acid in thelight-absorbing layer 10 is, for example, 3 to 180 parts by mass withrespect to 100 parts by mass of the matrix resin.

The matrix resin included in the light-absorbing layer 10 is, forexample, a (poly)olefin resin, polyimide resin, polyvinyl butyral resin,polycarbonate resin, polyamide resin, polysulfone resin,polyethersulfone resin, polyamideimide resin, (modified) acrylic resin,epoxy resin, or silicone resin. The matrix resin may contain an arylgroup such as a phenyl group and is desirably a silicone resincontaining an aryl group such as a phenyl group. If the light-absorbinglayer 10 is excessively hard, the likelihood of cure shrinkage-inducedcracking during the production process of the optical filter 1 aincreases with increasing thickness of the light-absorbing layer 10.When the matrix resin is a silicone resin containing an aryl group, thelight-absorbing layer 10 is likely to have high crack resistance.Moreover, with the use of a silicone resin containing an aryl group, thelight absorber formed by the above phosphonic acid and copper ion isless likely to be aggregated when included. Further, when the matrixresin of the light-absorbing layer 10 is a silicone resin containing anaryl group, it is desirable for the phosphoric acid ester included inthe light-absorbing layer 10 to have a flexible, linear organicfunctional group, such as an oxyalkyl group, just as does the phosphoricacid ester represented by the formula (c1) or formula (c2). This isbecause interaction derived from the combination of the above phosphonicacid, a silicone resin containing an aryl group, and phosphoric acidester having a linear organic functional group such as an oxyalkyl groupmakes aggregation of the light absorber less likely and can impart goodrigidity and good flexibility to the light-absorbing layer. Specificexamples of the silicone resin available as the matrix resin includeKR-255, KR-300, KR-2621-1, KR-211, KR-311, KR-216, KR-212, KR-251, andKR-5230. All of these are silicone resins manufactured by Shin-EtsuChemical Co., Ltd.

Examples of the hydrolytic polycondensation product of an alkoxysilanemonomer, the hydrolytic polycondensation product possibly being includedin the optical filter 1 a, include hydrolytic polycondensation productsof the following alkoxysilane monomers. The alkoxysilane monomers aretetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane,methyltriethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane,phenyltrimethoxysilane, phenyltriethoxysilane,3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, and3-glycidoxypropylmethyldiethoxysilane.

As shown in FIG. 1A, the optical filter 1 a further includes, forexample, a transparent dielectric substrate 20. One principal surface ofthe transparent dielectric substrate 20 is covered with thelight-absorbing layer 10. The characteristics of the transparentdielectric substrate 20 are not particularly limited as long as theoptical filter 1 a satisfies the above requirements (1) to (9) and therequirements ΔT_(S) ^(0/40) ₃₈₀₋₅₃₀≤3%, ΔT_(S) ^(0/40) ₄₅₀₋₆₅₀≤3%, andΔT_(S) ^(30/40) ₅₃₀₋₇₅₀≤3%. The transparent dielectric substrate 20 is,for example, a dielectric substrate having a high average transmittance(for example, 80% or more, preferably 85% or more, and more preferably90% or more) in the wavelength range of 450 nm to 600 nm.

The transparent dielectric substrate 20 is, for example, made of glassor resin. When the transparent dielectric substrate 20 is made of glass,the glass is, for example, borosilicate glass such as D 263 T eco,soda-lime glass (blue plate glass), white sheet glass such as B 270,alkali-free glass, or infrared-absorbing glass such as copper-containingphosphate glass or copper-containing fluorophosphate glass. When thetransparent dielectric substrate 20 is made of infrared-absorbing glasssuch as copper-containing phosphate glass or copper-containingfluorophosphate glass, the desired infrared absorption performance canbe imparted to the optical filter 1 a by a combination of the infraredabsorption performance of the transparent dielectric substrate 20 andthe infrared absorption performance of the light-absorbing layer 10.Examples of such an infrared-absorbing glass include BG-60, BG-61,BG-62, BG-63, and BG-67 manufactured by SCHOTT AG, 500EXL manufacturedby Nippon Electric Glass Co., Ltd., and CM5000, CM500, C5000, and C500Smanufactured by HOYA CORPORATION. Moreover, the transparent dielectricsubstrate 20 may have ultraviolet absorption characteristics.

The transparent dielectric substrate 20 may be a transparent crystallinesubstrate, such as magnesium oxide, sapphire, or quartz. For example,sapphire is very hard and is thus scratch resistant. Therefore, as ascratch-resistant protective material such as a protective filter orcover glass in an imaging apparatus, a sheet-shaped sapphire issometimes disposed ahead of a camera module or lens included in mobiledevices such as smartphones and mobile phones. Formation of thelight-absorbing layer 10 on such a sheet-shaped sapphire makes itpossible to protect camera modules and lenses and cut off unnecessarylight such as near infrared light.

When the transparent dielectric substrate 20 is made of resin, the resinis, for example, a (poly)olefin resin, polyimide resin, polyvinylbutyral resin, polycarbonate resin, polyamide resin, polysulfone resin,polyethersulfone resin, polyamideimide resin, (modified) acrylic resin,epoxy resin, or silicone resin.

The optical filter 1 a can be produced, for example, by applying acoating liquid for forming the light-absorbing layer 10 to one principalsurface of the transparent dielectric substrate 20 to form a film anddrying the film. The method for preparing the coating liquid and themethod for producing the optical filter 1 a will be described with anexample in which the light-absorbing layer 10 includes the lightabsorber formed by the phosphonic acid and copper ion.

First, an exemplary method for preparing the coating liquid will bedescribed. A copper salt such as copper acetate monohydrate is added toa given solvent such as tetrahydrofuran (THF), followed by stirring toobtain a copper salt solution. To this copper salt solution is thenadded a phosphoric acid ester compound such as a phosphoric acid diesterrepresented by the formula (c1) or a phosphoric acid monoesterrepresented by the formula (c2), followed by stirring to prepare asolution A. The first phosphonic acid is added to a given solvent suchas THF, followed by stirring to prepare a solution B. When the solutionB includes a plurality of first phosphonic acids, the solution B may beprepared by adding each of the phosphonic acids to a given solvent suchas THF, stirring each of the resultant mixtures, and mixing theplurality of liquids thus prepared. When the optical filter 1 a includesthe hydrolytic polycondensation product of the alkoxysilane monomer, forexample, the alkoxysilane monomer is further added to prepare thesolution B.

Next, the solution B is added to the solution A while the solution A isstirred, and the mixture is further stirred for a given period of time.To the resultant solution is then added a given solvent such as toluene,followed by stirring to obtain a solution C. Subsequently, the solutionC is subjected to solvent removal under heating for a given period oftime to obtain a solution D. This process removes the solvent such asTHF and the component such as acetic acid (boiling point: about 118° C.)generated by disassociation of the copper salt and yields a lightabsorber formed by the first phosphonic acid and copper ion. Thetemperature at which the solution C is heated is chosen based on theboiling point of the to-be-removed component disassociated from thecopper salt. During the solvent removal, the solvent such as toluene(boiling point: about 110° C.) used to obtain the solution C is alsoevaporated. A certain amount of this solvent desirably remains in thecoating liquid. This is preferably taken into account in determining theamount of the solvent to be added and the time period of the solventremoval. To obtain the solution C, o-xylene (boiling point: about 144°C.) may be used instead of toluene. In this case, the amount of o-xyleneto be added can be reduced to about one-fourth of the amount of tolueneto be added, because the boiling point of o-xylene is higher than theboiling point of toluene. A matrix resin such as a silicone resin isadded to the solution D, followed by stirring. The coating liquid canthus be prepared.

The coating liquid is applied to one principal surface of thetransparent dielectric substrate 20 to form a film. For example, thecoating liquid is applied to one principal surface of the transparentdielectric substrate 20 by die coating or spin coating or with adispenser to form a film. Next, this film is cured by a given heattreatment. For example, the film is exposed to an environment at atemperature of 50° C. to 200° C. for a given period of time.

The coating liquid may further contain the second phosphonic acid. Inthis case, the coating liquid is prepared, for example, by mixing andstirring the solution D, a solution H containing the second phosphonicacid, and a matrix resin. The solution H can be prepared, for example,in the following manner.

A copper salt such as copper acetate monohydrate is added to a givensolvent such as tetrahydrofuran (THF), followed by stirring to obtain acopper salt solution. To this copper salt solution is then added aphosphoric acid ester compound such as a phosphoric acid diesterrepresented by the formula (c1) or a phosphoric acid monoesterrepresented by the formula (c2), followed by stirring to prepare asolution E. The second phosphonic acid is added to a given solvent suchas THF, followed by stirring to prepare a solution F. Next, the solutionF is added to the solution E while the solution E is stirred, and themixture is further stirred for a given period of time. To the resultantsolution is then added a given solvent such as toluene, followed bystirring to obtain a solution G. Subsequently, the solution G issubjected to solvent removal under heating for a given period of time toobtain a solution H.

The light-absorbing layer 10 of the optical filter 1 a may be formed asa single layer or may be formed as a plurality of layers. When thelight-absorbing layer 10 is formed as a plurality of layers, thelight-absorbing layer 10 includes, for example, a first layer includingthe light absorber formed by the first phosphonic acid and copper ionand a second layer including the light absorber formed by the secondphosphonic acid and copper ion. In this case, a coating liquid forforming the first layer can be obtained by adding a matrix resin such asa silicone resin to the solution D and stirring the mixture. The secondlayer is formed using a coating liquid prepared separately from thecoating liquid for forming the first layer. The coating liquid forforming the second layer can be obtained, for example, by adding amatrix resin such as a silicone resin to the solution H and stirring themixture.

The first and second layers can be formed by applying the coating liquidfor forming the first layer and that for forming the second layer toform films, which are cured by a given heat treatment. For example, thefilms are exposed to an environment at a temperature of 50° C. to 200°C. for a given period of time. The order of forming the first and secondlayers is not particularly limited. The first and second layers may beformed in different time periods, or may be formed in the same timeperiod. A protective layer may be formed between the first and secondlayers. The protective layer is formed of, for example, a SiO₂-depositedfilm.

Modifications

The optical filter 1 a can be modified in various respects. For example,the optical filter 1 a may be modified to optical filters 1 b to 1 eshown in FIG. 1B to FIG. 1E. The optical filters 1 b to 1 e areconfigured in the same manner as the optical filter 1 a, unlessotherwise described. The components of the optical filters 1 b to 1 ethat are the same as or correspond to those of the optical filter 1 aare denoted by the same reference characters, and detailed descriptionsof such components are omitted. The description given for the opticalfilter 1 a can apply to the optical filters 1 b to 1 e, unless there istechnical inconsistency.

As shown in FIG. 1B, the optical filter 1 b has the light-absorbinglayers 10 formed on both principal surfaces of the transparentdielectric substrate 20. Therefore, the above requirements (1) to (9)and the requirements ΔT_(S) ^(0/40) ₃₈₀₋₅₃₀≤3%, ΔT_(S) ^(0/40)₄₅₀₋₆₅₀≤3%, and ΔT_(S) ^(0/40) ₅₃₀₋₇₅₀≤3% are satisfied not by onelight-absorbing layer 10 but by the two light-absorbing layers 10separated by the transparent dielectric substrate 20. Thelight-absorbing layers 10 on both principal surfaces of the transparentdielectric substrate 20 may have the same or different thicknesses. Thatis, the formation of the light-absorbing layers 10 on both principalsurfaces of the transparent dielectric substrate 20 is done so that thetwo light-absorbing layers 10 account for equal or unequal proportionsof the light-absorbing layer thickness required for the optical filter 1b to have desired optical characteristics. Thus, each of thelight-absorbing layers 10 formed on both principal surfaces of thetransparent dielectric substrate 20 of the optical filter 1 b has asmaller thickness than the thickness of the light-absorbing layer 10 ofthe optical filter 1 a. The formation of the light-absorbing layers 10on both principal surfaces of the transparent dielectric substrate 20can reduce warping of the optical filter 1 b even when the transparentdielectric substrate 20 is thin. Each of the two light-absorbing layers10 may be formed as a plurality of layers.

As shown in FIG. 1C, the optical filter 1 c has the light-absorbinglayers 10 formed on both principal surfaces of the transparentdielectric substrate 20. The optical filter 1 c additionally includes ananti-reflection film 30. The anti-reflection film 30 is a film formed asan interface between the optical filter 1 c and air and reducingreflection of visible light. The anti-reflection film 30 is, forexample, a film formed of a dielectric made of, for example, a resin, anoxide, or a fluoride. The anti-reflection film 30 may be a multilayerfilm formed by laminating two or more types of dielectrics havingdifferent refractive indices. The anti-reflection film 30 may be,particularly, a dielectric multilayer film made of alow-refractive-index material such as SiO₂ and a high-refractive-indexmaterial such as TiO₂ or Ta₂O₅. In this case, Fresnel reflection at theinterface between the optical filter 1 c and air is reduced and theamount of visible light transmitted through the optical filter 1 c canbe increased. The anti-reflection film 30 may be formed on both sides ofthe optical filter 1 c, or may be formed on one side thereof.

As shown in FIG. 1D, the optical filter 1 d consists only of thelight-absorbing layer 10. The optical filter 1 d can be produced, forexample, by applying the coating liquid onto a given substrate such as aglass substrate, resin substrate, or metal substrate (such as a steelsubstrate or stainless steel substrate) to form a film, curing the film,and then separating the film from the substrate. The optical filter 1 dmay be produced by casting. Not including the transparent dielectricsubstrate 20, the optical filter 1 d is thin. The optical filter 1 d canthus contribute more to achievement of lower-profile imagingapparatuses.

As shown in FIG. 1E, the optical filter le includes the light-absorbinglayer 10 and a pair of the anti-reflection films 30 disposed on bothsides of the light-absorbing layer 10. In this case, the optical filter1 e can contribute to achievement of lower-profile imaging apparatusesand can increase the amount of visible light transmitted therethroughmore than the optical filter 1 d can.

The optical filters 1 a to 1 e may be modified to include aninfrared-absorbing layer (not shown) in addition to the light-absorbinglayer 10, if necessary. The infrared-absorbing layer includes, forexample, an organic infrared absorber, such as a cyanine-based,phthalocyanine-based, squarylium-based, diimmonium-based, or azo-basedinfrared absorber or an infrared absorber composed of a metal complex.The infrared-absorbing layer includes, for example, one infraredabsorber or two or more infrared absorbers selected from these infraredabsorbers. The organic infrared absorber can absorb light in arelatively narrow wavelength range (absorption band) and is suitable forabsorbing light with a given wavelength range.

The optical filters 1 a to 1 e may be modified to include anultraviolet-absorbing layer (not shown) in addition to thelight-absorbing layer 10, if necessary. The ultraviolet-absorbing layerincludes, for example, an ultraviolet absorber, such as abenzophenone-based, triazine-based, indole-based, merocyanine-based, oroxazole-based ultraviolet absorber. The ultraviolet-absorbing layer, forexample, includes one ultraviolet absorber or two or more ultravioletabsorbers selected from these ultraviolet absorbers. The ultravioletabsorber can include ultraviolet absorbers that absorbs ultravioletlight with a wavelength around, for example, 300 nm to 340 nm, emitslight (fluorescence) with a wavelength longer than the absorbedwavelength, and functions as a fluorescent agent or fluorescentbrightener. The ultraviolet-absorbing layer can reduce incidence ofultraviolet light which deteriorates the materials, such as resin, usedin the optical filter.

The above infrared absorber and/or ultraviolet absorber may be containedbeforehand in the transparent dielectric substrate 20 made of resin toform a substrate having characteristics of absorbing infrared lightand/or ultraviolet light. In this case, it is necessary for the resin toallow the infrared absorber and/or ultraviolet absorber to beappropriately dissolved or dispersed therein and be transparent.Examples of such a resin include a (poly)olefin resin, polyimide resin,polyvinyl butyral resin, polycarbonate resin, polyamide resin,polysulfone resin, polyethersulfone resin, polyamideimide resin,(modified) acrylic resin, epoxy resin, and silicone resin.

As shown in FIG. 2, the optical filter 1 a is used to produce, forexample, an imaging apparatus 100 (camera module). The imaging apparatus100 includes a lens system 2, an imaging device 4, and the opticalfilter 1 a. Since the optical filter la satisfies the above requirements(1) to (9) and the requirements ΔT_(S) ^(0/40) ₃₈₀₋₅₃₀≤3%, ΔT_(S)^(0/40) ₄₅₀₋₆₅₀≤3%, and ΔT_(S) ^(0/40) ₅₃₀₋₇₅₀≤3%, an image generated bythe imaging apparatus 100 is unlikely to be colored unevenly.

As shown in FIG. 2, the imaging apparatus 100 further includes, forexample, a color filter 3 that is disposed ahead of the imaging device 4and is a filter of three colors, R (red), G (green), and B (blue). Theoptical filter 1 a is disposed ahead of the color filter 3. The colorfilter 3 and imaging device 4 receive light having been transmittedthrough the lens system 2. The light-absorbing layer 10 is, for example,arranged to be in contact with a side of the transparent dielectricsubstrate 20, the side being closer to the lens system 2. As describedpreviously, the protecting effect on the lens system 2 or imaging device4 increases when a hard material such as sapphire is used as thetransparent dielectric substrate 20. For example, in the color filter 3,the three colors, R (red), G (green), and B (blue), are arranged in amatrix, and any one of the R (red), G (green), and B (blue) colors isdisposed immediately above a sub-pixel of the imaging device 4. Theimaging device 4 receives light coming from an object and having beentransmitted through the lens system 2, optical filter 1 a, and colorfilter 3. The imaging apparatus 100 generates an image based oninformation on electric charge produced by the light received by theimaging device 4. The color filter 3 and imaging device 4 may becombined to configure a color image sensor.

The imaging apparatus 100 may be modified so that the optical filter 1 awill be disposed adjacent to the color filter 3. The imaging apparatus100 may also be modified to include at least one of the optical filters1 b to 1 e instead of the optical filter 1 a or in addition to theoptical filter 1 a.

EXAMPLES

The present invention will be described in more detail by examples. Thepresent invention is not limited to the examples given below.

Measurement of Transmittance Spectra

Transmittance spectra shown upon incidence of light with wavelengths of300 to 1200 nm on optical filters according to Examples and ComparativeExamples, intermediate products of some of the optical filters accordingto Examples and Comparative Examples, and laminates according toReference Examples were measured using an ultraviolet-visiblespectrophotometer (manufactured by JASCO Corporation, product name:V-670). In the transmittance spectrum measurement, the incident angle ofincident light was set to at least any one of 0°, 30°, 35°, 40°, 45°,50°, 55°, 60°, and 65°. From the results of the measurement of thetransmittance spectrum shown by each of the optical filters according toExamples and Comparative Examples at each incident angle, a spectraltransmittance curve (normalized spectral transmittance curve) normalizedso that the maximum of the spectral transmittance in the wavelengthrange of 400 to 650 nm would be 100% was obtained for each incidentangle. Based on the normalized spectral transmittance curves for theincident angles, an average ΔT_(S) ^(x/y) _(W-V) of absolute values ofdifferences each between a value of a normalized spectral transmittancefor the incident angle x° and a value of a normalized spectraltransmittance for the incident angle y° in the wavelength range of W nmto V nm (W<V) was calculated.

Example 1

1.125 g of copper acetate monohydrate ((CH₃COO)₂Cu.H₂O) and 60 g oftetrahydrofuran (THF) were mixed and stirred for 3 hours to obtain acopper acetate solution. To the obtained copper acetate solution wasthen added 0.412 g of PLYSURF A208N (manufactured by DKS Co., Ltd.)which is a phosphoric acid ester compound, followed by stirring for 30minutes to obtain a solution A. 10 g of THF was added to 0.176 g ofphenylphosphonic acid (C₆H₅PO(OH)₂) (manufactured by Nissan ChemicalIndustries, Ltd.), followed by stirring for 30 minutes to obtain asolution B1-1. 10 g of THF was added to 1.058 g of4-bromophenylphosphonic acid (C₆H₄BrPO(OH)₂) (manufactured by TokyoChemical Industry Co., Ltd.), followed by stirring for 30 minutes toobtain a solution B1-2. Next, the solutions B1-1 and B1-2 were mixed andstirred for 1 minute. 2.166 g of methyltriethoxysilane (MTES:CH₃Si(OC₂H₅)₃) (manufactured by Shin-Etsu Chemical Co., Ltd.) and 0.710g of tetraethoxysilane (TEOS: Si(OC₂H₅)₄) (manufactured by KISHIDACHEMICAL Co., Ltd., special grade) were added, and the mixture wasfurther stirred for 1 minute to obtain a solution B1. The solution B1was added to the solution A while the solution A was stirred, and themixture was stirred at room temperature for 1 minute. To the resultantsolution was then added 25 g of toluene, followed by stirring at roomtemperature for 1 minute to obtain a solution C1. The solution C1 wasplaced in a flask and subjected to solvent removal using a rotaryevaporator (manufactured by Tokyo Rikakikai Co., Ltd., product code:N-1110SF) under heating by means of an oil bath (manufactured by TokyoRikakikai Co., Ltd., product code: OSB-2100). The temperature of the oilbath was controlled to 105° C. The solution having undergone the solventremoval was then collected from the flask. A solution D1 was thusobtained. The solution D1 was a dispersion of fine particles of copperphenyl-based phosphonate (light absorber) including copperphenylphosphonate and copper 4-bromophenylphosphonate. The solution D1was transparent, and the fine particles of the light absorber were welldispersed therein.

1.125 g of copper acetate monohydrate and 36 g of THF were mixed andstirred for 3 hours to obtain a copper acetate solution. To the obtainedcopper acetate solution was then added 0.643 g of PLYSURF A208N which isa phosphoric acid ester compound, followed by stirring for 30 minutes toobtain a solution E1. 10 g of THF was added to 0.722 g ofn-butylphosphonic acid (C₄H₉PO(OH)₂) (manufactured by Nippon ChemicalIndustrial Co., Ltd.), followed by stirring for 30 minutes to obtain asolution F1. The solution F1 was added to the solution E1 while thesolution E1 was stirred, and the mixture was stirred at room temperaturefor 1 minute. To the resultant solution was then added 25 g of toluene,followed by stirring at room temperature for 1 minute to obtain asolution G1. The solution G1 was placed in a flask and subjected tosolvent removal using a rotary evaporator under heating by means of anoil bath. The temperature of the oil bath was controlled to 105° C. Thesolution having undergone the solvent removal was then collected fromthe flask. A solution H1 was thus obtained. The solution H1 was adispersion of fine particles of copper butylphosphonate. The solution H1was transparent, and the fine particles were well dispersed therein.

To the solution D1 was added 2.200 g of a silicone resin (manufacturedby Shin-Etsu Chemical Co., Ltd., product name: KR-300), followed bystirring for 30 minutes to obtain a solution I1. The solution H1 wasadded to the solution I1, followed by stirring for 30 minutes to obtaina light-absorbing composition according to Example 1.

The light-absorbing composition according to Example 1 was applied witha dispenser to a 30 mm×30 mm central region of each surface of atransparent glass substrate (manufactured by SCHOTT AG, product name: D263 T eco) made of borosilicate glass and having dimensions of 76 mm×76mm×0.07 mm. Films were thus formed on the substrate. When thelight-absorbing composition was applied to the transparent glasssubstrate, a frame having an opening corresponding in dimensions to theregion where the film-forming liquid was applied was put on thetransparent glass substrate to hold back the film-forming liquid andprevent the film-forming liquid from spreading. After the application toone surface of the transparent glass substrate, the transparent glasssubstrate was left at ordinary temperature until the appliedlight-absorbing composition lost its flowability. Then, thelight-absorbing composition was applied also to the other surface of thetransparent glass substrate in the same manner. The amount of thelight-absorbing composition applied was determined so that the sum ofthe thicknesses of the layers which were originally the light-absorbingcomposition films and were formed on both surfaces of the transparentglass substrate would eventually be about 180 μm. Subsequently, thetransparent glass substrate with the undried light-absorbing compositionfilms was placed in an oven and heat-treated at 85° C. for 6 hours tocure the film. After that, the transparent glass substrate with thefilms formed thereon was placed in a thermo-hygrostat set at atemperature of 85° C. and a relative humidity of 85% for a 20-hourhumidification treatment. The humidification treatment was performed topromote hydrolysis and polycondensation of the alkoxysilane monomercontained in the light-absorbing composition applied onto thetransparent glass substrate and form a hard and dense matrix of eachlight-absorbing layer. After that, a region with the light-absorbinglayers formed on the transparent glass substrate was cut out to obtainan optical filter according to Example 1. The sum of the thicknesses ofthe light-absorbing layers on both surfaces of the optical filteraccording to Example 1 is 183 μm. Transmittance spectra shown by theoptical filter according to Example 1 at incident angles of 0°, 30°,35°, 40°, 45°, 50°, 55°, 60°, and 65° are shown in FIGS. 3A and 3B.Values of characteristics derived from the transmittance spectrum shownby the optical filter according to Example 1 at an incident angle of 0°are shown in Table 3. Normalized spectral transmittance curves shown bythe optical filter according to Example 1 at incident angles of 0°, 30°,35°, 40°, 45°, 50°, 55°, 60°, and 65° are shown in FIGS. 4A and 4B.Values of ΔT_(S) ^(0/y) _(W-V) of the optical filter according toExample 1 for an incident angle x° of 0° and values of ΔT_(S) ^(30/y)_(W-V) of the optical filter according to Example 1 for an incidentangle x° of 30° are shown in Tables 4 and 5, respectively.

As shown in Table 3, the above requirements (1) to (9) are satisfied bythe optical filter according to Example 1. As shown in Tables 4 and 5,the values of ΔT_(S) ^(0/y) _(W-V) and ΔT_(S) ^(30/y) _(W-V) of theoptical filter according to Example 1 satisfy the requirements shown inTables 1 and 2, respectively. For the optical filter according toExample 1, as shown in FIGS. 3A and 3B, the transmittances in awavelength region of 380 nm or less and a wavelength region of 700 nm ormore are sufficiently low, and the transmittances at a wavelength of 450nm and in the wavelength range of 500 to 600 nm are sufficiently high.In other words, the optical filter according to Example 1 can favorablyblock light in the ultraviolet and near-infrared regions and hascharacteristics of allowing light in the visible region to betransmitted sufficiently. For the optical filter according to Example 1,as shown in FIGS. 4A and 4B, the normalized spectral transmittances forincident angles of 0° to 65° are sufficiently low in a wavelength regionof 380 nm or less and a wavelength region of 700 nm or more, and thenormalized spectral transmittances for incident angles of 0° to 65° aresufficiently high at a wavelength of 450 nm and in the wavelength rangeof 500 to 600 nm. Therefore, the optical filter according to Example 1favorably blocks light in the ultraviolet and near-infrared regions andhas advantageous characteristics for sufficiently transmitting light inthe visible region, even when sensitivity correction is made so as tocover a decrease in the amount of light in accordance with the angle oflight assumed from a design viewpoint to be incident on an imagingdevice in an imaging apparatus. Additionally, each gap between theshapes of one and another of the normalized spectral transmittancecurves shown by the optical filter according to Example 1 at theincident angles is small, and an image generated by an imaging apparatusemploying the optical filter according to Example 1 is deemed to beunlikely to be colored unevenly.

Example 2

1.125 g of copper acetate monohydrate ((CH₃COO)₂Cu.H₂O) and 60 g oftetrahydrofuran (THF) were mixed and stirred for 3 hours to obtain acopper acetate solution. To the obtained copper acetate solution wasthen added 0.412 g of PLYSURF A208N (manufactured by DKS Co., Ltd.)which is a phosphoric acid ester compound, followed by stirring for 30minutes to obtain a solution A. 10 g of THF was added to 0.441 g ofphenylphosphonic acid (C₆H₅PO(OH)₂) (manufactured by Nissan ChemicalIndustries, Ltd.), followed by stirring for 30 minutes to obtain asolution B2-1. 10 g of THF was added to 0.661 g of4-bromophenylphosphonic acid (C₆H₄BrPO(OH)₂) (manufactured by TokyoChemical Industry Co., Ltd.), followed by stirring for 30 minutes toobtain a solution B2-2. Next, the solutions B2-1 and B2-2 were mixed andstirred for 1 minute. 1.934 g of methyltriethoxysilane (MTES:CH₃Si(OC₂H₅)₃) (manufactured by Shin-Etsu Chemical Co., Ltd.) and 0.634g of tetraethoxysilane (TEOS: Si(OC₂H₅)₄) (manufactured by KISHIDACHEMICAL Co., Ltd., special grade) were added, and the mixture wasfurther stirred for 1 minute to obtain a solution B2. The solution B2was added to the solution A while the solution A was stirred, and themixture was stirred at room temperature for 1 minute. To the resultantsolution was then added 25 g of toluene, followed by stirring at roomtemperature for 1 minute to obtain a solution C2. The solution C2 wasplaced in a flask and subjected to solvent removal using a rotaryevaporator (manufactured by Tokyo Rikakikai Co., Ltd., product code:N-1110SF) under heating by means of an oil bath (manufactured by TokyoRikakikai Co., Ltd., product code: OSB-2100). The temperature of the oilbath was controlled to 105° C. The solution having undergone the solventremoval was then collected from the flask. A solution D2 was thusobtained. The solution D2 was a dispersion of fine particles of copperphenyl-based phosphonate (light absorber) including copperphenylphosphonate and copper 4-bromophenylphosphonate. The solution D2was transparent, and the fine particles were well dispersed therein.

1.125 g of copper acetate monohydrate and 36 g of THF were mixed andstirred for 3 hours to obtain a copper acetate solution. To the obtainedcopper acetate solution was then added 0.710 g of PLYSURF A208N which isa phosphoric acid ester compound, followed by stirring for 30 minutes toobtain a solution E2. 10 g of THF was added to 0.708 g ofn-butylphosphonic acid (C₄H₉PO(OH)₂) (manufactured by Nippon ChemicalIndustrial Co., Ltd.), followed by stirring for 30 minutes to obtain asolution F2. The solution F2 was added to the solution E2 while thesolution E2 was stirred, and the mixture was stirred at room temperaturefor 1 minute. To the resultant solution was then added 25 g of toluene,followed by stirring at room temperature for 1 minute to obtain asolution G2. This solution G2 was placed in a flask and subjected tosolvent removal using a rotary evaporator under heating by means of anoil bath. The temperature of the oil bath was controlled to 105° C. Thesolution having undergone the solvent removal was then collected fromthe flask. A solution H2 was thus obtained. The solution H2 was adispersion of fine particles of copper butylphosphonate. The solution H2was transparent, and the fine particles were well dispersed therein.

To the solution D2 was added 2.200 g of a silicone resin (manufacturedby Shin-Etsu Chemical Co., Ltd., product name: KR-300), followed bystirring for 30 minutes to obtain a solution I2. The solution H2 wasadded to the solution I2, followed by stirring for 30 minutes to obtaina light-absorbing composition according to Example 2.

The light-absorbing composition according to Example 2 was applied witha dispenser to a 30 mm×30 mm central region of one principal surface ofa transparent glass substrate (manufactured by SCHOTT AG, product name:D 263 T eco) made of borosilicate glass and having dimensions of 76mm×76 mm×0.21 mm. A film was thus formed on the substrate. When thelight-absorbing composition was applied to the transparent glasssubstrate, a frame having an opening corresponding in dimensions to theregion where the film-forming liquid was applied was put on thetransparent glass substrate to hold back the film-forming liquid andprevent the film-forming liquid from spreading. The amount of thelight-absorbing composition applied was determined so that the thicknessof the layer which was originally the light-absorbing composition filmwould eventually be about 170 μm. Subsequently, the transparent glasssubstrate with the undried light-absorbing composition film was placedin an oven and heat-treated at 85° C. for 6 hours to cure the film.After that, the transparent glass substrate with the film formed thereonwas placed in a thermo-hygrostat set at a temperature of 85° C. and arelative humidity of 85% for a 20-hour humidification treatment. Anoptical filter according to Example 2 including a light-absorbing layerformed on a transparent glass substrate was thus obtained. Thehumidification treatment was performed to promote hydrolysis andpolycondensation of the alkoxysilane monomer contained in thelight-absorbing composition applied onto the transparent glass substrateand form a hard and dense matrix of the light-absorbing layer. Afterthat, a region with the light-absorbing layer formed on a transparentglass substrate was cut out to obtain the optical filter according toExample 2. The thickness of the light-absorbing layer of the opticalfilter according to Example 2 is 170 μm. Transmittance spectra shown bythe optical filter according to Example 2 at incident angles of 0°, 30°,35°, 40°, 45°, 50°, 55°, 60°, and 65° are shown in FIGS. 5A and 5B.Values of characteristics derived from the transmittance spectrum shownby the optical filter according to Example 2 at an incident angle of 0°are shown in Table 6. Normalized spectral transmittance curves shown bythe optical filter according to Example 2 at incident angles of 0°, 30°,35°, 4°, 45°, 50°, 55°, 60°, and 65° are shown in FIGS. 6A and 6B.Values of ΔT_(S) ^(0/y) _(W-V) of the optical filter according toExample 2 for an incident angle x° of 0° and values of ΔT_(S) ^(30/y)_(W-V) of the optical filter according to Example 2 for an incidentangle x° of 30° are shown in Table 7 and Table 8, respectively.

As shown in Table 6, the above requirements (1) to (9) are satisfied bythe optical filter according to Example 2. As shown in Tables 7 and 8,the values of ΔT_(S) ^(0/y) _(W-V) and ΔT_(S) ^(30/y) _(W-V) of theoptical filter according to Example 2 satisfy the requirements shown inTables 1 and 2, respectively. As shown in FIGS. 5A and 5B, the opticalfilter according to Example 2 has transmission bands extending to ashort wavelength side compared to the transmission bands of the opticalfilter according to Example 1, and has transmittances slightly less than20% at a wavelength of 380 nm. According to Japanese IndustrialStandards (JIS) Z 8120, the short-wavelength limit in the wavelengthrange of an electromagnetic wave equivalent to a visible ray is 360 to400 nm. It can be said that the transmittance of the optical filteraccording to Example 2 sharply increases around the short-wavelengthlimit of a visible ray with increase in wavelength. For the opticalfilter according to Example 2, transmission of a small amount of lightwas observed in a band of more than 1100 nm. In this band, however,common imaging devices have a low sensitivity. Therefore, incorporatingthe optical filter according to Example 2 in an imaging apparatus is notconsidered problematic in practical use.

For the optical filter according to Example 2, the transmittances in awavelength region of less than 380 nm and a wavelength region of 700 nmor more, exclusive of a wavelength region of 1100 nm or more, aresufficiently low and the transmittances at a wavelength of 450 nm and inthe wavelength range of 500 to 600 nm are sufficiently high. The opticalfilter according to Example 2 can favorably block light in theultraviolet and near-infrared regions and has characteristics ofallowing light in the visible region to be transmitted sufficiently. Forthe optical filter according to Example 2, as shown in FIGS. 6A and 6B,the normalized spectral transmittances for incident angles of 0° to 65°are sufficiently low in a wavelength region of less than 380 nm and awavelength region of 700 nm or more exclusive of a wavelength region of1100 nm or more, and the normalized spectral transmittances for incidentangles of 0° to 65° are sufficiently high at a wavelength of 450 nm andin the wavelength range of 500 to 600 nm. Therefore, the optical filteraccording to Example 2 favorably blocks light in the ultraviolet andnear-infrared regions and has advantageous characteristics forsufficiently transmitting light in the visible region, even whensensitivity correction is made so as to cover a decrease in the amountof light in accordance with the angle of light assumed from a designviewpoint to be incident on an imaging device in an imaging apparatus.Additionally, each gap between the shapes of one and another of thenormalized spectral transmittance curves shown by the optical filteraccording to Example 2 at the incident angles is small, and an imagegenerated by an imaging apparatus employing the optical filter accordingto Example 2 is deemed to be unlikely to be colored unevenly. Theoptical filter according to Example 2 includes the light-absorbing layeronly on one surface of the transparent glass substrate. Therefore, inorder to reduce warping of the transparent glass substrate due to stressin the light-absorbing layer, the transparent glass substrate is thickerthan the transparent glass substrate of the optical filter according toExample 1. In other words, the thickness of a transparent glasssubstrate is easily reduced by formation of a light-absorbing layer oneach surface of the transparent glass substrate, as in the opticalfilter according to Example 1.

Example 3

1.125 g of copper acetate monohydrate ((CH₃COO)₂Cu.H₂O) and 60 g oftetrahydrofuran (THF) were mixed and stirred for 3 hours to obtain acopper acetate solution. To the obtained copper acetate solution wasthen added 0.412 g of PLYSURF A208N (manufactured by DKS Co., Ltd.)which is a phosphoric acid ester compound, followed by stirring for 30minutes to obtain a solution A. 10 g of THF was added to 0.176 g ofphenylphosphonic acid (C₆H₅PO(OH)₂) (manufactured by Nissan ChemicalIndustries, Ltd.), followed by stirring for 30 minutes to obtain asolution B3-1. 10 g of THF was added to 1.058 g of4-bromophenylphosphonic acid (C₆H₄BrPO(OH)₂) (manufactured by TokyoChemical Industry Co., Ltd.), followed by stirring for 30 minutes toobtain a solution B3-2. Next, the solutions B3-1 and B3-2 were mixed andstirred for 1 minute. 2.166 g of methyltriethoxysilane (MTES:CH₃Si(OC₂H₅)₃) (manufactured by Shin-Etsu Chemical Co., Ltd.) and 0.710g of tetraethoxysilane (TEOS: Si(OC₂H₅)₄) (manufactured by KISHIDACHEMICAL Co., Ltd., special grade) were added, and the mixture wasfurther stirred for 1 minute to obtain a solution B3. The solution B3was added to the solution A while the solution A was stirred, and themixture was stirred at room temperature for 1 minute. To the resultantsolution was then added 25 g of toluene, followed by stirring at roomtemperature for 1 minute to obtain a solution C3. This solution C3 wasplaced in a flask and subjected to solvent removal using a rotaryevaporator (manufactured by Tokyo Rikakikai Co., Ltd., product code:N-1110SF) under heating by means of an oil bath (manufactured by TokyoRikakikai Co., Ltd., product code: OSB-2100). The temperature of the oilbath was controlled to 105° C. The solution having undergone the solventremoval was then collected from the flask. A solution D3 was thusobtained. The solution D3 was a dispersion of fine particles of copperphenyl-based phosphonate (light absorber) including copperphenylphosphonate and copper 4-bromophenylphosphonate. The solution D3was transparent, and the fine particles were well dispersed therein.

1.125 g of copper acetate monohydrate and 36 g of THF were mixed andstirred for 3 hours to obtain a copper acetate solution. To the obtainedcopper acetate solution was then added 0.643 g of PLYSURF A208N which isa phosphoric acid ester compound, followed by stirring for 30 minutes toobtain a solution E3. 10 g of THF was added to 0.722 g ofn-butylphosphonic acid (C₄H₉PO(OH)₂) (manufactured by Nippon ChemicalIndustrial Co., Ltd.), followed by stirring for 30 minutes to obtain asolution F3. The solution F3 was added to the solution E3 while thesolution E3 was stirred, and the mixture was stirred at room temperaturefor 1 minute. To the resultant solution was then added 25 g of toluene,followed by stirring at room temperature for 1 minute to obtain asolution G3. This solution G3 was placed in a flask and subjected tosolvent removal using a rotary evaporator under heating by means of anoil bath. The temperature of the oil bath was controlled to 105° C. Thesolution having undergone the solvent removal was then collected fromthe flask. A solution H3 was thus obtained. The solution H3 was adispersion of fine particles of copper butylphosphonate. The solution H3was transparent, and the fine particles were well dispersed therein.

To the solution D3 was added 2.200 g of a silicone resin (manufacturedby Shin-Etsu Chemical Co., Ltd., product name: KR-300), followed bystirring for 30 minutes to obtain a solution I3. The solution H3 wasadded to the solution I3, followed by stirring for 30 minutes to obtaina light-absorbing composition according to Example 3.

The light-absorbing composition according to Example 3 was applied witha dispenser to a 30 mm×30 mm central region of one surface of atransparent glass substrate (manufactured by SCHOTT AG, product name: D263 T eco) made of borosilicate glass and having dimensions of 76 mm×76mm×0.21 mm. A film was thus formed on the substrate. When thelight-absorbing composition was applied to the transparent glasssubstrate, a frame having an opening corresponding in dimensions to theregion where the film-forming liquid was applied was put on thetransparent glass substrate to hold back the film-forming liquid andprevent the film-forming liquid from spreading. The amount of thelight-absorbing composition applied was determined so that the thicknessof the layer which was originally the light-absorbing composition filmwould eventually be about 135 μm. Subsequently, the transparent glasssubstrate with the undried film was placed in an oven and heat-treatedat 85° C. for 6 hours to cure the film. After that, the transparentglass substrate with the film formed thereon was placed in athermo-hygrostat set at a temperature of 85° C. and a relative humidityof 85% for a 20-hour humidification treatment to form a light-absorbinglayer on the transparent glass substrate. The humidification treatmentwas performed to promote hydrolysis and polycondensation of thealkoxysilane monomer contained in the light-absorbing compositionapplied onto the transparent glass substrate and form a hard and densematrix of the light-absorbing layer. The light-absorbing layer on thetransparent glass substrate thus obtained was peeled off to obtain anoptical filter according to Example 3. The thickness of the opticalfilter according to Example 3 is 135 μm. Transmittance spectra shown bythe optical filter according to Example 3 at incident angles of 0°, 30°,35°, 40°, 45°, 50°, 5°, 60°, and 65° are shown in FIGS. 7A and 7B.Values of characteristics derived from the transmittance spectrum shownby the optical filter according to Example 3 at an incident angle of 0°are shown in Table 9. Normalized spectral transmittance curves shown bythe optical filter according to Example 3 at incident angles of 0°, 30°,35°, 40°, 45°, 50°, 5°, 60°, and 65° are shown in FIGS. 8A and 8B.Values of ΔT_(S) ^(0/y) _(W-V) of the optical filter according toExample 3 for an incident angle x° of 0° and values of ΔT_(S) ^(30/y)_(W-V) of the optical filter according to Example 3 for an incidentangle x° of 30° are shown in Tables 10 and 11, respectively.

As shown in Table 9, the above requirements (1) to (9) are satisfied bythe optical filter according to Example 3. As shown in Tables 10 and 11,the values of ΔT_(S) ^(0/y) _(W-V) and ΔT_(S) ^(30/y) _(W-V) of theoptical filter according to Example 3 satisfy the requirements shown inTables 1 and 2, respectively. For the optical filter according toExample 3, the transmittances at wavelengths of 700 nm and 715 nm arewithin the acceptable range, albeit slightly high compared to those forthe optical filters according to Examples 1 and 2. For the opticalfilter according to Example 3, transmission of a small amount of lightwas observed in a band of more than 1100 nm unlike in the case of theoptical filter according to Example 1, but the transmittance of light inthis band was suppressed compared to the case of the optical filteraccording to Example 2. In this band, common imaging devices have a lowsensitivity. Therefore, incorporating the optical filter according toExample 3 in an imaging apparatus is not considered problematic inpractical use. For the optical filter according to Example 3, thetransmittances in a wavelength region of 380 nm or less are sufficientlylow, and the transmittances at a wavelength of 450 nm and in thewavelength region of 500 to 600 nm are sufficiently high. In otherwords, the optical filter according to Example 3 can favorably blocklight in the ultraviolet and near-infrared regions and hascharacteristics of allowing light in the visible region to betransmitted sufficiently.

For the optical filter according to Example 3, as shown in FIGS. 8A and8B, the normalized spectral transmittances for incident angles of 0° to65° are sufficiently low in a wavelength region of 380 nm or less and awavelength region of 700 nm or more, and the normalized spectraltransmittances for incident angles of 0° to 65° are sufficiently high ata wavelength of 450 nm and in the wavelength range of 500 to 600 nm.Therefore, the optical filter according to Example 3 favorably blockslight in the ultraviolet and near-infrared regions and has advantageouscharacteristics for sufficiently transmitting light in the visibleregion, even when sensitivity correction is made so as to cover adecrease in the amount of light in accordance with the angle of lightassumed from a design viewpoint to be incident on an imaging device inan imaging apparatus. Additionally, each gap between the shapes of oneand another of the normalized spectral transmittance curves shown by theoptical filter according to Example 3 at the incident angles is small,and an image generated by an imaging apparatus employing the opticalfilter according to Example 3 is deemed to be unlikely to be coloredunevenly. Since the optical filter according to Example 3 does notinclude a transparent glass substrate and is composed only of alight-absorbing layer, the thickness of the optical filter can bereduced.

Example 4

1.1 g of copper acetate monohydrate and 60 g of tetrahydrofuran (THF)were mixed and stirred for 3 hours. To the obtained solution was added2.3 g of a phosphoric acid ester (manufactured by DKS Co., Ltd., productname: PLYSURF A208F), followed by stirring for 30 minutes to obtain asolution A4. 10 g of THF was added to 0.6 g of phenylphosphonic acid(manufactured by Tokyo Chemical Industry Co., Ltd.), followed bystirring for 30 minutes to obtain a solution B4. The solution B4 wasadded to the solution A4 while the solution A4 was stirred, and themixture was stirred at room temperature for 1 minute. To the resultantsolution was added 45 g of toluene, followed by stirring at roomtemperature for 1 minute to obtain a solution C4. The solution C4 wasplaced in a flask and subjected to solvent removal for 25 minutes usinga rotary evaporator (manufactured by Tokyo Rikakikai Co., Ltd., productcode: N-1110SF) under heating by means of an oil bath (manufactured byTokyo Rikakikai Co., Ltd., product code: OSB-2100) controlled to 120° C.The solution having undergone the solvent removal was taken out of theflask, and to the solution was added 4.4 g of a silicone resin(manufactured by Shin-Etsu Chemical Co., Ltd., product name: KR-300),followed by stirring at room temperature for 30 minutes to obtain alight-absorbing composition IRA1.

2.25 g of copper acetate monohydrate and 120 g of tetrahydrofuran (THF)were mixed and stirred for 3 hours. To the obtained solution was added1.8 g of a phosphoric acid ester (manufactured by DKS Co., Ltd., productname: PLYSURF A208F), followed by stirring for 30 minutes to obtain asolution E4. 20 g of THF was added to 1.35 g of butylphosphonic acid,followed by stirring for 30 minutes to obtain a solution F4. Thesolution F4 was added to the solution E4 while the solution E4 wasstirred, and the mixture was stirred at room temperature for 3 hours. Tothe resultant solution was added 40 g of toluene, and the solvent wasevaporated in an 85° C. environment over 7.5 hours. To the resultantsolution was added 8.8 g of a silicone resin (manufactured by Shin-EtsuChemical Co., Ltd., product name: KR-300), followed by stirring for 3hours to obtain a light-absorbing composition IRA2.

The light-absorbing composition IRA1 obtained was applied to oneprincipal surface of a transparent glass substrate (manufactured bySCHOTT AG, product name: D 263 T eco) using a die coater. The resultantfilm was cured by heat treatment in an oven at 85° C. for 3 hours, at125° C. for 3 hours, at 150° C. for 1 hour, and then at 170° C. for 3hours to form a light-absorbing layer frail. The light-absorbingcomposition IRA1 was applied in the same manner to the other principalsurface of the transparent glass substrate. The resultant film was curedunder the same conditions as the conditions for forming thelight-absorbing layer frail to form a light-absorbing layer ira12. Thetotal thickness of the light-absorbing layer frail and light-absorbinglayer ira12 is 0.2 mm. An intermediate product a was thus obtained. Atransmittance spectrum obtained upon incidence of light with awavelength of 300 to 1200 nm on the intermediate product a at anincident angle of 0° is shown in FIG. 9A. In this transmittancespectrum, the spectral transmittance at a wavelength of 380 nm is 10.9%,the spectral transmittance at a wavelength of 450 nm is 85.7%, theaverage of the spectral transmittance in the wavelength range of 500 to600 nm is 88.1%, the spectral transmittance at a wavelength of 700 nm is2.3%, the spectral transmittance at a wavelength of 715 nm is 0.9%, theaverage of the spectral transmittance in the wavelength range of 700 to800 nm is 0.4%, the maximum of the spectral transmittance in thewavelength range of 750 to 1080 nm is 7.6%, and the maximum of thespectral transmittance in the wavelength range of 1000 to 1100 nm is12.1%.

A 500-nm-thick SiO₂ film was vapor-deposited on the light-absorbinglayer frail and light-absorbing layer ira12 using a vacuum depositionapparatus to form a protective layer p1 and protective layer p2,respectively. The light-absorbing composition IRA2 was applied onto thesurface of the protective layer p1 with a die coater. The resultant filmwas cured by heat treatment in an oven at 85° C. for 3 hours, at 125° C.for 3 hours, at 150° C. for 1 hour, and then at 170° C. for 3 hours toform a light-absorbing layer ira21. The light-absorbing composition IRA2was applied also onto the protective layer p2. The resultant film wascured under the same heating conditions as the conditions for formingthe light-absorbing layer ira21 to form a light-absorbing layer ira22.The total thickness of the light-absorbing layer ira21 andlight-absorbing layer ira22 is 50 μm. An intermediate product 13 wasthus obtained. A transmittance spectrum obtained upon incidence of lightwith a wavelength of 300 to 1200 nm on the intermediate product 13 at anincident angle of 0° is shown in FIG. 9B. In this transmittancespectrum, the spectral transmittance at a wavelength of 380 nm is 10.5%,the spectral transmittance at a wavelength of 450 nm is 84.0%, theaverage of the spectral transmittance in the wavelength range of 500 to600 nm is 87.2%, the spectral transmittance at a wavelength of 700 nm is1.8%, the spectral transmittance at a wavelength of 715 nm is 0.6%, theaverage of the spectral transmittance in the wavelength range of 700 to800 nm is 0.3%, the maximum of the spectral transmittance in thewavelength range of 750 to 1080 nm is 0.7%, and the maximum of thespectral transmittance in the wavelength range of 1000 to 1100 nm is1.2%.

A 500-nm-thick SiO₂ film was vapor-deposited on the infrared-absorbinglayer ira22 using a vacuum deposition apparatus to form a protectivelayer p3.

To a solution containing MEK as a solvent and an ultraviolet-absorbingsubstance composed of a benzophenone-based ultraviolet-absorbingsubstance which has low light absorption in the visible region and issoluble in methyl ethyl ketone (MEK) was added polyvinyl butyral (PVB)in an amount equivalent to 60 weight % of the solids of the solution,followed by stirring for 2 hours to obtain a light-absorbing compositionUVA1.

The light-absorbing composition UVA1 was applied onto the protectivelayer p3 by spin coating, followed by curing of the resultant film byheating at 140° C. for 30 minutes to form a light-absorbing layer uva1.The thickness of the light-absorbing layer uva1 is 6 μm. Separately, a6-μm-thick light-absorbing layer uva1 was formed on one principalsurface of a transparent glass substrate (manufactured by SCHOTT AG,product name: D 263 T eco) using the light-absorbing composition UVA1 toobtain a laminate according to Reference Example 1. A transmittancespectrum obtained upon incidence of light with a wavelength of 300 to1200 nm on the laminate according to Reference Example 1 at an incidentangle of 0° is shown in FIG. 9C.

An anti-reflection film ar1 and anti-reflection film ar2 were formed onthe light-absorbing layer ira21 and light-absorbing layer uva1,respectively, by vacuum deposition. The specifications of theanti-reflection film ar1 and anti-reflection film ar2 were the same.Each of the anti-reflection film ar1 and anti-reflection film ar2 was afilm composed of SiO₂ and TiO₂ that were alternately laminated. Each ofthe anti-reflection film ar1 and anti-reflection film ar2 included sevenlayers and had a total thickness of about 0.4 μm. An optical filteraccording to Example 4 was thus obtained. Additionally, ananti-reflection film an was formed on one surface of a transparent glasssubstrate (manufactured by SCHOTT AG, product name: D 263 T eco) toobtain a laminate according to Reference Example 2. Transmittancespectra obtained upon incidence of light with a wavelength of 300 to1200 nm on the laminate according to Reference Example 2 at incidentangles of 0°, 30°, 50° and 65° are shown in FIG. 9D. For the laminateaccording to Reference Example 2, as shown in FIG. 9D, a wavelength bandincluding a local transmittance decrease does not exist in thewavelength range of 400 to 700 nm for any of the incident angles.

Transmittance spectra shown by the optical filter according to Example 4at incident angles of 0°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, and 65° areshown in FIGS. 10A and 10B. Values of characteristics derived from thetransmittance spectrum shown by the optical filter according to Example4 at an incident angle of 0° are shown in Table 12. Normalized spectraltransmittance curves shown by the optical filter according to Example 4at incident angles of 0°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, and 65° areshown in FIGS. 11A and 11B. Values of ΔT_(S) ^(0/y) _(W-V) of theoptical filter according to Example 4 for an incident angle x° of 0° andvalues of ΔT_(S) ^(30/y) _(W-V) of the optical filter according toExample 4 for an incident angle x° of 30° are shown in Tables 13 and 14,respectively.

As shown in Table 12, the above requirements (1) to (9) are satisfied bythe optical filter according to Example 4. As shown in Tables 13 and 14,the values of ΔT_(S) ^(0/y) _(W-V) and ΔT_(S) ^(30/y) _(W-V) of theoptical filter according to Example 4 satisfy the requirements shown inTables 1 and 2, respectively. For the optical filter according toExample 4, the transmittances in a wavelength region of 380 nm or lessand a wavelength region of 700 nm or more are sufficiently low, and thetransmittances at a wavelength of 450 nm and in the wavelength region of500 to 600 nm are sufficiently high. In other words, the optical filteraccording to Example 4 can favorably block light in the ultraviolet andnear-infrared regions and has characteristics of allowing light in thevisible region to be transmitted sufficiently. Moreover, since theoptical filter according to Example 4 includes the anti-reflection film,the optical filter according to Example 4 has high transmittances in thevisible region compared to those of the optical filters according toExamples 1 to 3 in the visible region. Additionally, no ripple occurs inthe wavelength range of 400 to 700 nm upon incidence of light on theoptical filter according to Example 4 at incident angles of 0° to 65°.Furthermore, since the optical filter according to Example 4 includesthe light-absorbing layer uva1, the transmittance sharply increasesaround 400 nm with increase in wavelength.

For the optical filter according to Example 4, as shown in FIGS. 11A and11B, the normalized spectral transmittances for incident angles of 0° to65° are sufficiently low in a wavelength region of 380 nm or less and awavelength region of 700 nm or more, and the normalized spectraltransmittances for incident angles of 0° to 65° are sufficiently high ata wavelength of 450 nm and in the wavelength range of 500 to 600 nm.Therefore, the optical filter according to Example 4 favorably blockslight in the ultraviolet and near-infrared regions and has advantageouscharacteristics for sufficiently transmitting light in the visibleregion, even when sensitivity correction is made so as to cover adecrease in the amount of light in accordance with the angle of lightassumed from a design viewpoint to be incident on an imaging device inan imaging apparatus. Additionally, each gap between the shapes of oneand another of the normalized spectral transmittance curves shown by theoptical filter according to Example 4 at the incident angles is small,and an image generated by an imaging apparatus employing the opticalfilter according to Example 4 is deemed to be unlikely to be coloredunevenly.

Comparative Example 1

A light-reflecting layer irr1 that reflects light with a wavelength inthe range of 730 to 1100 nm was formed on one principal surface of atransparent glass substrate (manufactured by SCHOTT AG, product name: D263 T eco) by alternately laminating SiO₂ and TiO₂ in 50 layers using avacuum deposition apparatus. An intermediate product y was thusobtained. Transmittance spectra obtained upon incidence of light with awavelength of 300 to 1200 nm on the intermediate product Y at incidentangles of 0°, 30° and 50° are shown in FIG. 12A. In the transmittancespectrum for an incident angle of 0°, the spectral transmittance at awavelength of 380 nm is less than 0.2%, the spectral transmittance at awavelength of 450 nm is 94.8%, the average of the spectral transmittancein the wavelength range of 500 to 600 nm is 94.3%, the spectraltransmittance at a wavelength of 700 nm is 62.8%, the spectraltransmittance at a wavelength of 715 nm is 9.5%, the average of thespectral transmittance in the wavelength range of 700 to 800 nm is 6.1%,the maximum of the spectral transmittance in the wavelength range of 750to 1080 nm is 1.0%, and the maximum of the spectral transmittance in thewavelength range of 1000 to 1100 nm is 0.5%. In the transmittancespectrum for an incident angle of 30°, the spectral transmittance at awavelength of 380 nm is less than 0.2%, the spectral transmittance at awavelength of 450 nm is 94.6%, the average of the spectral transmittancein the wavelength range of 500 to 600 nm is 93.3%, the spectraltransmittance at a wavelength of 700 nm is 3.2%, the spectraltransmittance at a wavelength of 715 nm is 1.4%, the average of thespectral transmittance in the wavelength range of 700 to 800 nm is 1.0%,the maximum of the spectral transmittance in the wavelength range of 750to 1080 nm is 0.8%, and the maximum of the spectral transmittance in thewavelength range of 1000 to 1100 nm is 0.6%. In the transmittancespectrum for an incident angle of 50°, the spectral transmittance at awavelength of 380 nm is 3.7%, the spectral transmittance at a wavelengthof 450 nm is 84.0%, the average of the spectral transmittance in thewavelength range of 500 to 600 nm is 86.0%, the spectral transmittanceat a wavelength of 700 nm is 1.6%, the spectral transmittance at awavelength of 715 nm is 1.1%, the average of the spectral transmittancein the wavelength range of 700 to 800 nm is 0.9%, the maximum of thespectral transmittance in the wavelength range of 750 to 1080 nm is6.8%, and the maximum of the spectral transmittance in the wavelengthrange of 1000 to 1100 nm is 12.7%.

A cyanine-based organic dye and squarylium-based organic dye which aresoluble in MEK were added to MEK serving as a solvent to prepare asolution. PVB in an amount equivalent to 99 weight % of the solids ofthe solution was added to the solution, followed by stirring for 2 hoursto obtain a coating liquid. This coating liquid was applied by spincoating onto a principal surface of the transparent glass substrate ofthe intermediate product y, the principal surface opposite to theprincipal surface on which the light-reflecting layer irr1 was formed,and the resultant film was cured by heating at 140° C. for 30 minutes toform a light-absorbing layer ira3. Separately, a light-absorbing layerira3 was formed in the same manner on one principal surface of atransparent glass substrate (manufactured by SCHOTT AG, product name: D263 T eco) to obtain a laminate according to Reference Example 3. Atransmittance spectrum obtained upon incidence of light with awavelength of 300 to 1200 nm on the laminate according to ReferenceExample 3 at an incident angle of 0° is shown in FIG. 12B. In thistransmittance spectrum, the spectral transmittance at a wavelength of380 nm is 80.1%, the spectral transmittance at a wavelength of 450 nm is83.8%, the average of the spectral transmittance in the wavelength rangeof 500 to 600 nm is 86.9%, the spectral transmittance at a wavelength of700 nm is 2.0%, the spectral transmittance at a wavelength of 715 nm is2.6%, the average of the spectral transmittance in the wavelength rangeof 700 to 800 nm is 15.9%, the maximum of the spectral transmittance inthe wavelength range of 750 to 1080 nm is 90.2%, and the maximum of thespectral transmittance in the wavelength range of 1000 to 1100 nm is91.1%.

An anti-reflection film ar1 was formed on the light-absorbing layer ira3by vacuum deposition according to the same specifications as those ofthe anti-reflection film ar1 of the optical filter according to Example4. An optical filter according to Comparative Example 1 was fabricatedin this manner.

Transmittance spectra shown by the optical filter according toComparative Example 1 at incident angles of 0°, 30°, 35°, 40°, 45°, 50°,55°, 60°, and 65° are shown in FIGS. 13A and 13B. Values ofcharacteristics derived from the transmittance spectrum shown by theoptical filter according to Comparative Example 1 at an incident angleof 0° are shown in Table 15. Normalized spectral transmittance curvesshown by the optical filter according to Comparative Example 1 atincident angles of 0°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, and 65° areshown in FIGS. 14A and 14B. Values of ΔT_(S) ^(0/y) _(W-V) of theoptical filter according to Comparative Example 1 for an incident anglex° of 0° and values of ΔT_(S) ^(30/y) _(W-V) of the optical filteraccording to Comparative Example 1 for an incident angle x° of 30° areshown in Tables 16 and 17, respectively.

As shown in Table 15, the optical filter according to ComparativeExample 1 satisfies the above requirements (1) to (9). However, as shownin Table 16, the values of ΔT_(S) ^(0/y) _(W-V) of the optical filteraccording to Comparative Example 1 do not satisfy the requirements shownin Table 1, except for ΔT_(S) ^(0/30) ₄₅₀₋₆₅₀, ΔT_(S) ^(0/30) ₅₃₀₋₇₅₀,and ΔT_(S) ^(0/35) ₄₅₀₋₆₅₀. As shown in Table 17, the values of ΔT_(S)^(30/y) _(W-V) of the optical filter according to Comparative Example 1do not satisfy the requirements shown in Table 2, except for ΔT_(S)^(30/35) ₄₅₀₋₆₅₀, ΔT_(S) ^(30/35) ₆₅₀₋₁₂₀₀. As shown in Tables 13A and13B, the influence of a shift of the reflection band of thelight-reflecting layer irr1 to the short wavelength side grows withincrease in incident angle of light incident on the optical filteraccording to Comparative Example 1. Additionally, a large ripple occursaround 500 nm. Therefore, many of the values of ΔT_(S) ^(0/y) _(W-V) andΔT_(S) ^(30/y) _(W-V) of the optical filter according to ComparativeExample 1 greatly exceed the upper limits shown in Tables 1 and 2.

The optical filter according to Comparative Example 1 blocks light inthe near-infrared region not only by the action of the light-absorbinglayer but also by the action of the light-reflecting layer. Thelight-reflecting layer exhibits its function of reflecting light by aninterference effect attributed to its multilayer film. Thus, incidenceof light at a large incident angle larger than a design value resultsnot only in a shift of a wavelength band of reflected light to the shortwavelength side but also in a ripple in a wavelength band of light whichshould be transmitted and severe distortion of the resultant spectraltransmittance curve. Therefore, although the transmittance spectrum oflight vertically incident on the optical filter according to ComparativeExample 1 satisfies the desired requirements, the transmittance spectraof light incident thereon at larger incident angles cannot satisfy thedesired requirements. Therefore, when an imaging apparatus in which theoptical filter according to Comparative Example 1 is incorporated isused to take an object at a wide angle of view, for example, for awide-angle shot, it is difficult to reproduce an even color tone of theobject in the image taken and there is also concern that the imageobtained may be colored quite unevenly.

Comparative Example 2

A light-absorbing transparent substrate bg1 was prepared. Atransmittance spectrum obtained upon incidence of light with awavelength of 300 to 1200 nm on the light-absorbing transparentsubstrate bg1 at an incident angle of 0° is shown in FIG. 15A. In thistransmittance spectrum, the spectral transmittance at a wavelength of380 nm is 86.8%, the spectral transmittance at a wavelength of 450 nm is90.2%, the average of the spectral transmittance in the wavelength rangeof 500 to 600 nm is 86.5%, the spectral transmittance at a wavelength of700 nm is 29.8%, the spectral transmittance at a wavelength of 715 nm is25.3%, the average of the spectral transmittance in the wavelength rangeof 700 to 800 nm is 19.1%, the maximum of the spectral transmittance inthe wavelength range of 750 to 1080 nm is 30.2%, and the maximum of thespectral transmittance in the wavelength range of 1000 to 1100 nm is32.5%.

A light-reflecting layer irr2 that reflects light in the wavelengthrange of 720 to 1100 nm were formed on one principal surface of thelight-absorbing transparent substrate bg1 by alternately laminating SiO₂and TiO₂ in 54 layers using a vacuum deposition apparatus. Separately, alight-reflecting layer irr2 was formed in the same manner on oneprincipal surface of a transparent glass substrate (manufactured bySCHOTT AG, product name: D 263 T eco) to fabricate a laminate accordingto Reference Example 4. Transmittance spectra obtained upon incidence oflight with a wavelength of 300 to 1200 nm on the laminate according toReference Example 4 at incident angles of 0°, 30°, and 50° are shown inFIG. 15B. In the transmittance spectrum for an incident angle 0°, thespectral transmittance at a wavelength of 380 nm is less than 0.2%, thespectral transmittance at a wavelength of 450 nm is 94.3%, the averageof the spectral transmittance in the wavelength range of 500 to 600 nmis 94.7%, the spectral transmittance at a wavelength of 700 nm is 73.5%,the spectral transmittance at a wavelength of 715 nm is 9.8%, theaverage of the spectral transmittance in the wavelength range of 700 to800 nm is 6.7%, the maximum of the spectral transmittance in thewavelength range of 750 to 1080 nm is 0.7%, and the maximum of thespectral transmittance in the wavelength range of 1000 to 1100 nm is0.3%. In the transmittance spectrum for an incident angle of 30°, thespectral transmittance at a wavelength of 380 nm is 1.6%, the spectraltransmittance at a wavelength of 450 nm is 90.8%, the averagetransmittance in the wavelength range of 500 to 600 nm is 93.2%, thespectral transmittance at a wavelength of 700 nm is 2.7%, the spectraltransmittance at a wavelength of 715 nm is 1.1%, the average of thespectral transmittance in the wavelength range of 700 to 800 nm is 0.8%,the maximum of the spectral transmittance in the wavelength range of 750to 1080 nm is 0.7%, and the maximum of the spectral transmittance in thewavelength range of 1000 to 1100 nm is 1.0%. In the transmittancespectrum for an incident angle of 50°, the spectral transmittance at awavelength of 380 nm is 49.4%, the spectral transmittance at awavelength of 450 nm is 87.5%, the average of the spectral transmittancein the wavelength range of 500 to 600 nm is 89.8%, the spectraltransmittance at a wavelength of 700 nm is 1.6%, the spectraltransmittance at a wavelength of 715 nm is 0.8%, the average of thespectral transmittance in the wavelength range of 700 to 800 nm is 0.9%,the maximum of the spectral transmittance in the wavelength range of 750to 1080 nm is 6.0%, and the maximum of the spectral transmittance in thewavelength range of 1000 to 1100 nm is 13.0%.

A benzophenone-based ultraviolet-absorbing substance having low lightabsorption in the visible region and soluble in MEK was used as anultraviolet absorber, and an infrared-absorbing dye composed of asquarylium compound and cyanine compound was used as an infraredabsorber. The ultraviolet absorber and infrared absorber were weighedand added to MEK serving as a solvent to prepare a solution. PVB in anamount equivalent to 99 weight % of the solids of the solution was addedto the solution, followed by stirring for 2 hours to obtain a coatingliquid. This coating liquid was applied to the other principal surfaceof the light-absorbing transparent substrate bg1 to form alight-absorbing layer uvira2. A light-absorbing layer uvira2 was formedin the same manner on one principal surface of a transparent glasssubstrate (manufactured by SCHOTT AG, product name: D 263 T eco) toobtain a laminate according to Reference Example 5. A transmittancespectrum shown upon incidence of light with a wavelength of 300 to 1200nm on the laminate according to Reference Example 5 at an incident angleof 0° is shown in FIG. 15C. In this transmittance spectrum, the spectraltransmittance at a wavelength of 380 nm is less than 0.2%, the spectraltransmittance at a wavelength of 450 nm is 84.3%, the average of thespectral transmittance in the wavelength range of 500 to 600 nm is88.7%, the spectral transmittance at a wavelength of 700 nm is 4.8%, thespectral transmittance at a wavelength of 715 nm is 8.4%, the average ofthe spectral transmittance in the wavelength range of 700 to 800 nm is63.8%, the maximum of the spectral transmittance in the wavelength rangeof 750 to 1080 nm is 92.7%, and the maximum of the spectraltransmittance in the wavelength range of 1000 to 1100 nm is 92.7%.

An anti-reflection film art was formed on the light-absorbing layeruvira2 formed on the other principal surface of the light-absorbingtransparent substrate bg1 by vacuum deposition according to the samespecifications as those of the anti-reflection film ar1 of the opticalfilter according to Example 4. An optical filter according toComparative Example 2 was fabricated in this manner.

Transmittance spectra shown by the optical filter according toComparative Example 2 at incident angles of 0°, 30°, 35°, 40°, 45°, 50°,55°, 60°, and 65° are shown in FIGS. 16A and 16B. Values ofcharacteristics derived from the transmittance spectrum shown by theoptical filter according to Comparative Example 2 at an incident angleof 0° are shown in Table 18. Normalized spectral transmittance curvesshown by the optical filter according to Comparative Example 2 atincident angles of 0°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, and 65° areshown in FIGS. 17A and 17B. Values of ΔT_(S) ^(0/y) _(W-V) of theoptical filter according to Comparative Example 2 for an incident anglex° of 0° and values of ΔT_(S) ^(30/y) _(W-V) of the optical filteraccording to Comparative Example 2 for an incident angle x° of 30° areshown in Tables 19 and 20, respectively.

As shown in Table 18, the optical filter according to ComparativeExample 2 satisfies the above requirements (1) to (9). However, as shownin Table 19, the values of ΔT_(S) ^(0/y) _(W-V) of the optical filteraccording to Comparative Example 2 do not satisfy the requirements shownin Table 1, except for ΔT_(S) ^(0/30) ₃₈₀₋₅₃₀, ΔT_(S) ^(0/30) ₄₅₀₋₆₅₀,ΔT_(S) ^(0/30) ₅₃₀₋₇₅₀, ΔT_(S) ^(0/30) ₆₅₀₋₁₂₀₀, ΔT_(S) ^(0/30)₃₈₀₋₁₂₀₀, ΔT_(S) ^(0/35) ₄₅₀₋₆₅₀, and ΔT_(S) ^(0/35) ₅₃₀₋₇₅₀. As shownin Table 20, the values of ΔT_(S) ^(30/y) _(W-V) of the optical filteraccording to Comparative Example 2 do not satisfy the requirements shownin Table 2, except for ΔT_(S) ^(30/35) ₃₈₀₋₅₃₀, ΔT_(S) ^(30/35) ₄₅₀₋₆₅₀,ΔT_(S) ^(30/35) ₅₃₀₋₇₅₀, ΔT_(S) ^(30/35) ₆₅₀₋₁₂₀₀, ΔT_(S) ^(30/35)₃₈₀₋₁₂₀₀, and ΔT_(S) ^(30/35) ₅₃₀₋₇₅₀. As shown in Tables 16A and 16B,the influence of a shift of the reflection band of the light-reflectinglayer irr2 to the short wavelength side grows with increase in incidentangle of light incident on the optical filter according to ComparativeExample 2. Additionally, a large ripple occurs around 500 nm. Therefore,many of the values of ΔT_(S) ^(0/y) _(W-V) and ΔT_(S) ^(30/y) _(W-V) ofthe optical filter according to Comparative Example 2 greatly exceed theupper limits shown in Tables 1 and 2.

For the optical filter according to Comparative Example 2, in both thenear-infrared and ultraviolet regions, the boundary between a wavelengthband of light expected to be transmitted and a wavelength band of lightexpected to be blocked is determined by light absorption. Thelight-reflecting layer exhibits its function of reflecting light by aninterference effect attributed to its multilayer film. Thus, incidenceof light at a large incident angle larger than a design value resultsnot only in a shift of a wavelength band of reflected light to the shortwavelength side but also in a ripple in a wavelength band of light whichshould be transmitted and severe distortion of the resultant spectraltransmittance curve. For the optical filter according to ComparativeExample 2, a narrow absorption band achieved by the light-absorbinglayer in the near-infrared region results in failure to set the blockingband achieved by the light-reflecting layer on a sufficiently longwavelength side. Thus, the influence of the shift of the reflection bandto the short wavelength side with increase in incident angle of light isinevitable for the optical filter according to Comparative Example 2. Asa result, although the transmittance spectrum of light verticallyincident on the optical filter according to Comparative Example 2satisfies the desired requirements, the transmittance spectra of lightincident thereon at larger incident angles cannot satisfy the desiredrequirements. When an imaging apparatus in which the optical filteraccording to Comparative Example 2 is incorporated is used to take anobject at a wide angle of view, for example, for a wide-angle shot, itis difficult to reproduce an even color tone of the object in the imagetaken and there is also concern that the image obtained may be coloredquite unevenly.

TABLE 3 (1) Spectral transmittance at wavelength of 380 nm 1.0% (2)Spectral transmittance at wavelength of 450 nm 81.4% (3) Average ofspectral transmittance in wavelength 86.0% range of 500 nm to 600 nm (4)Spectral transmittance at wavelength of 700 nm 2.3% (5) Spectraltransmittance at wavelength of 715 nm 0.8% (6) Average of spectraltransmittance in wavelength 0.3% range of 700 nm to 800 nm (7) Maximumof spectral transmittance in wavelength <0.2% range of 750 nm to 1080 nm(8) Maximum of spectral transmittance in wavelength <0.2% range of 1000nm to 1100 nm (9) Wavelength bandwidth in which spectral 177 nmtransmittance is 75% or more between wavelengths of 400 nm and 700 nm

TABLE 4 ΔTs^(0/y)W-V y = 30° y = 35° y = 40° y = 45° y = 50° y = 55° y =60° y = 65° W = 380 nm; V = 530 nm   0.8%   1.0% 1.2% 1.9% 2.0% 1.8%2.8% 4.1% W = 450 nm; V = 650 nm   0.4%   0.6% 0.7% 1.1% 1.2% 1.3% 2.2%2.7% W = 530 nm; V = 750 nm   0.6%   0.8% 1.1% 1.4% 1.5% 1.9% 2.6% 3.2%W = 650 nm; V = 1200 nm <0.2% <0.2% 0.2% 0.3% 0.3% 0.3% 0.4% 0.5% W =380 nm; V = 1200 nm   0.3%   0.4% 0.5% 0.7% 0.8% 0.8% 1.2% 1.6%

TABLE 5 ΔTs^(30/y)W-V y = 35° y = 40° y = 45° y = 50° y = 55° y = 60° y= 65° W = 380 nm; V = 530 nm   0.2%   0.5%   1.1%   1.2% 1.3% 2.2% 3.3%W = 450 nm; V = 650 nm <0.2%   0.3%   0.6%   0.7% 1.0% 1.9% 2.3% W = 530nm; V = 750 nm   0.2%   0.5%   0.7%   0.9% 1.3% 1.9% 2.6% W = 650 nm; V= 1200 nm <0.2% <0.2% <0.2% <0.2% 0.2% 0.3% 0.4% W = 380 nm; V = 1200 nm<0.2%   0.2%   0.4%   0.5% 0.6% 0.9% 1.3%

TABLE 6 (1) Spectral transmittance at wavelength of 380 nm 17.3% (2)Spectral transmittance at wavelength of 450 nm 83.6% (3) Average ofspectral transmittance in wavelength 85.6% range of 500 nm to 600 nm (4)Spectral transmittance at wavelength of 700 nm 2.2% (5) Spectraltransmittance at wavelength of 715 nm 0.8% (6) Average of spectraltransmittance in wavelength 0.4% range of 700 nm to 800 nm (7) Maximumof spectral transmittance in wavelength 1.0% range of 750 nm to 1080 nm(8) Maximum of spectral transmittance in wavelength 1.6% range of 1000nm to 1100 nm (9) Wavelength bandwidth in which spectral 192 nmtransmittance is 75% or more between wavelengths of 400 nm and 700 nm

TABLE 7 ΔTs^(0/y)W-V y = 30° y = 35° y = 40° y = 45° y = 50° y = 55° y =60° y = 65° W = 380 nm; V = 530 nm   0.4% 0.5% 0.6% 0.6% 1.0% 2.0% 3.6%4.5% W = 450 nm; V = 650 nm   0.5% 0.5% 0.7% 0.9% 1.1% 1.3% 1.8% 2.2% W= 530 nm; V = 750 nm   0.6% 0.7% 1.0% 1.3% 1.5% 1.7% 1.8% 1.9% W = 650nm; V = 1200 nm <0.2% 0.3% 0.3% 0.4% 0.5% 0.5% 0.6% 0.6% W = 380 nm; V =1200 nm   0.3% 0.4% 0.5% 0.6% 0.7% 1.0% 1.3% 1.5%

TABLE 8 ΔTs^(30/y)W-V y = 35° y = 40° y = 45° y = 50° y = 55° y = 60° y= 65° W = 380 nm; V = 530 nm <0.2%   0.3% 0.4% 0.7% 1.6% 3.2% 4.0% W =450 nm; V = 650 nm <0.2%   0.3% 0.5% 0.7% 0.9% 1.3% 1.7% W = 530 nm; V =750 nm <0.2%   0.4% 0.7% 1.0% 1.2% 1.3% 1.4% W = 650 nm; V = 1200 nm<0.2% <0.2% 0.2% 0.3% 0.4% 0.4% 0.4% W = 380 nm; V = 1200 nm <0.2%  0.2% 0.3% 0.5% 0.7% 1.0% 1.2%

TABLE 9 (1) Spectral transmittance at wavelength of 380 nm 1.5% (2)Spectral transmittance at wavelength of 450 nm 78.5% (3) Average ofspectral transmittance in wavelength 85.0% range of 500 nm to 600 nm (4)Spectral transmittance at wavelength of 700 nm 4.8% (5) Spectraltransmittance at wavelength of 715 nm 2.2% (6) Average of spectraltransmittance in wavelength 0.9% range of 700 nm to 800 nm (7) Maximumof spectral transmittance in wavelength 0.4% range of 750 nm to 1080 nm(8) Maximum of spectral transmittance in wavelength 0.7% range of 1000nm to 1100 nm (9) Wavelength bandwidth in which spectral 173 nmtransmittance is 75% or more between wavelengths of 400 nm and 700 nm

TABLE 10 ΔTs^(0/y)W-V y = 30° y = 35° y = 40° y = 45° y = 50° y = 55° y= 60° y = 65° W = 380 nm; V = 530 nm 0.8% 0.9% 1.1% 1.5% 1.9% 2.2% 2.5%2.9% W = 450 nm; V = 650 nm 0.3% 0.5% 0.6% 0.7% 0.9% 1.0% 1.1% 1.2% W =530 nm; V = 750 nm 0.6% 0.8% 1.0% 1.2% 1.4% 1.6% 1.7% 1.8% W = 650 nm; V= 1200 nm 0.2% 0.3% 0.3% 0.4% 0.4% 0.5% 0.5% 0.5% W = 380 nm; V = 1200nm 0.3% 0.4% 0.5% 0.7% 0.8% 0.9% 1.0% 1.0%

TABLE 11 ΔTs^(30/y)W-V y = 35° y = 40° y = 45° y = 50° y = 55° y = 60° y= 65° W = 380 nm; V = 530 nm <0.2%   0.4%   0.7% 1.1% 1.4% 1.7% 2.1% W =450 nm; V = 650 nm <0.2%   0.3%   0.4% 0.6% 0.7% 0.7% 0.9% W = 530 nm; V= 750 nm   0.2%   0.5%   0.7% 0.9% 1.0% 1.1% 1.2% W = 650 nm; V = 1200nm <0.2% <0.2% <0.2% 0.2% 0.3% 0.3% 0.3% W = 380 nm; V = 1200 nm <0.2%  0.2%   0.3% 0.5% 0.6% 0.7% 0.7%

TABLE 12 (1) Spectral transmittance at wavelength of 380 nm <0.2% (2)Spectral transmittance at wavelength of 450 nm 82.5% (3) Average ofspectral transmittance in wavelength 89.5% range of 500 nm to 600 nm (4)Spectral transmittance at wavelength of 700 nm 1.9% (5) Spectraltransmittance at wavelength of 715 nm 0.7% (6) Average of spectraltransmittance in wavelength 0.3% range of 700 nm to 800 nm (7) Maximumof spectral transmittance in wavelength 0.6% range of 750 nm to 1080 nm(8) Maximum of spectral transmittance in wavelength 0.9% range of 1000nm to 1100 nm (9) Wavelength bandwidth in which spectral 183 nmtransmittance is 75% or more between wavelengths of 400 nm and 700 nm

TABLE 13 ΔTs^(0/y)W-V y = 30° y = 35° y = 40° y = 45° y = 50° y = 55° y= 60° y = 65° W = 380 nm; V = 530 nm 0.8% 1.1% 1.3% 1.5% 1.6% 1.6% 1.6%1.9% W = 450 nm; V = 650 nm 0.8% 1.1% 1.4% 1.7% 2.0% 2.2% 2.4% 2.7% W =530 nm; V = 750 nm 0.9% 1.2% 1.6% 2.0% 2.5% 2.9% 3.2% 3.4% W = 650 nm; V= 1200 nm 0.3% 0.4% 0.5% 0.6% 0.7% 0.8% 0.9% 0.9% W = 380 nm; V = 1200nm 0.5% 0.6% 0.8% 1.0% 1.2% 1.3% 1.4% 1.6%

TABLE 14 ΔTs^(30/y)W-V y = 35° y = 40° y = 45° y = 50° y = 55° y = 60° y= 65° W = 380 nm; V = 530 nm   0.3%   0.6% 0.8% 1.1% 1.2% 1.2% 1.3% W =450 nm; V = 650 nm   0.3%   0.7% 1.1% 1.4% 1.7% 1.9% 2.1% W = 530 nm; V= 750 nm   0.3%   0.7% 1.2% 1.6% 2.0% 2.3% 2.6% W = 650 nm; V = 1200 nm<0.2% <0.2% 0.3% 0.4% 0.5% 0.6% 0.6% W = 380 nm; V = 1200 nm <0.2%  0.4% 0.6% 0.7% 0.9% 1.0% 1.1%

TABLE 15 (1) Spectral transmittance at wavelength of 380 nm <0.2% (2)Spectral transmittance at wavelength of 450 nm 86.2% (3) Average ofspectral transmittance in wavelength 90.2% range of 500 nm to 600 nm (4)Spectral transmittance at wavelength of 700 nm 1.4% (5) Spectraltransmittance at wavelength of 715 nm 0.3% (6) Average of spectraltransmittance in wavelength 0.3% range of 700 nm to 800 nm (7) Maximumof spectral transmittance in wavelength 0.7% range of 750 nm to 1080 nm(8) Maximum of spectral transmittance in wavelength 0.5% range of 1000nm to 1100 nm (9) Wavelength bandwidth in which spectral 196 nmtransmittance is 75% or more between wavelengths of 400 nm and 700 nm

TABLE 16 ΔTs^(0/y)W-V y = 30° y = 35° y = 40° y = 45° y = 50° y = 55° y= 60° y = 65° W = 380 nm; V = 530 nm 6.9% 10.2% 12.7% 15.3% 17.6% 19.0%20.4% 22.5% W = 450 nm; V = 650 nm 1.7%  2.6%  4.0%  7.2% 11.7% 16.3%21.0% 25.1% W = 530 nm; V = 750 nm 2.3%  3.3%  4.8%  7.0%  9.7% 12.5%15.6% 18.3% W = 650 nm; V = 1200 nm 1.2%  2.0%  3.0%  4.1%  5.6%  6.9% 8.5% 11.0% W = 380 nm; V = 1200 nm 2.3%  3.5%  4.7%  6.3%  8.4% 10.2%12.3% 15.2%

TABLE 17 ΔTs^(30/y)W-V y = 35° y = 40° y = 45° y = 50° y = 55° y = 60° y= 65° W = 380 nm; V = 530 nm 4.1% 8.1% 12.4% 16.3% 18.4% 19.6% 20.0% W =450 nm; V = 650 nm 1.9% 3.5%  6.3% 11.2% 15.6% 20.0% 24.2% W = 530 nm; V= 750 nm 1.6% 3.2%  5.1%  7.9% 10.7% 13.5% 16.4% W = 650 nm; V = 1200 nm0.9% 1.9%  3.0%  4.6%  5.9%  7.4% 10.0% W = 380 nm; V = 1200 nm 1.5%3.1%  4.9%  7.3%  9.3% 11.3% 13.9%

TABLE 18 (1) Spectral transmittance at wavelength of 380 nm <0.2% (2)Spectral transmittance at wavelength of 450 nm 84.6% (3) Average ofspectral transmittance in wavelength 87.1% range of 500 nm to 600 nm (4)Spectral transmittance at wavelength of 700 nm 1.3% (5) Spectraltransmittance at wavelength of 715 nm 0.3% (6) Average of spectraltransmittance in wavelength 0.2% range of 700 nm to 800 nm (7) Maximumof spectral transmittance in wavelength <0.2% range of 750 nm to 1080 nm(8) Maximum of spectral transmittance in wavelength <0.2% range of 1000nm to 1100 nm (9) Wavelength bandwidth in which spectral 172 nmtransmittance is 75% or more between wavelengths of 400 nm and 700 nm

TABLE 19 ΔTs^(0/y)W-V y = 30° y = 35° y = 40° y = 45° y = 50° y = 55° y= 60° y = 65° W = 380 nm; V = 530 nm 1.9% 3.2% 5.4% 8.1% 10.8% 13.9%16.7% 17.7% W = 450 nm; V = 650 nm 1.7% 2.4% 4.2% 7.5% 11.0% 15.3% 19.9%22.2% W = 530 nm; V = 750 nm 1.9% 2.8% 4.3% 6.5%  8.6% 11.2% 14.2% 16.4%W = 650 nm; V = 1200 nm 0.7% 1.2% 1.8% 2.2%  2.7%  3.1%  3.3%  3.9% W =380 nm; V = 1200 nm 1.0% 1.6% 2.5% 3.7%  5.0%  6.5%  8.0%  9.1%

TABLE 20 ΔTs^(30/y)W-V y = 35° y = 40° y = 45° y = 50° y = 55° y = 60° y= 65° W = 380 nm; V = 530 nm 2.2% 4.3% 6.8%  9.8% 13.0% 15.6% 17.0% W =450 nm; V = 650 nm 1.7% 3.4% 6.2% 10.1% 14.5% 18.8% 21.4% W = 530 nm; V= 750 nm 1.3% 2.8% 4.6%  6.8%  9.5% 12.4% 14.6% W = 650 nm; V = 1200 nm0.5% 1.1% 1.5%  2.1%  2.4%  2.7%  3.2% W = 380 nm; V = 1200 nm 0.9% 1.8%2.9%  4.2%  5.7%  7.2%  8.3%

1. An optical filter comprising: a light-absorbing layer that includes alight absorber for absorbing light in at least a portion of thenear-infrared region, wherein when light with a wavelength of 300 to1200 nm is incident on the optical filter at an incident angle of 0°,the optical filter satisfies the following requirements (1) to (9): (1)a spectral transmittance at a wavelength of 380 nm is 20% or less; (2)the spectral transmittance at a wavelength of 450 nm is 75% or more; (3)an average of the spectral transmittance in the wavelength range of 500to 600 nm is 80% or more; (4) the spectral transmittance at a wavelengthof 700 nm is 5% or less; (5) the spectral transmittance at a wavelengthof 715 nm is 3% or less; (6) an average of the spectral transmittance inthe wavelength range of 700 to 800 nm is 1% or less; (7) the maximum ofthe spectral transmittance in the wavelength range of 750 to 1080 nm is1% or less; (8) the maximum of the spectral transmittance in thewavelength range of 1000 to 1100 nm is 2% or less; and (9) a wavelengthbandwidth of a wavelength band in which the spectral transmittance inthe wavelength range of 400 to 700 nm is 75% or more is 170 nm or more,and when light with a wavelength of 300 to 1200 nm is incident on theoptical filter at incident angles of x° and y° (0≤x≤30, 30≤y≤65, andx<y) and an average of absolute values of differences each between avalue of a normalized spectral transmittance for the incident angle x°and a value of a normalized spectral transmittance for the incidentangle y° at the same wavelength in the wavelength range of W nm to V nm(W<V) is expressed as ΔT_(S) ^(x/y) _(W-V), the optical filter satisfiesrequirements ΔT_(S) ^(0/40) ₃₈₀₋₅₃₀≤3%, ΔT_(S) ^(0/40) ₄₅₀₋₆₅₀≤3%, andΔT_(S) ^(0/40) ₅₃₀₋₇₅₀≤3%. the normalized spectral transmittance beingdetermined by normalization of a spectral transmittance for each of theincident angles so that the maximum of the spectral transmittance foreach of the incident angles in the wavelength range of 400 to 650 nm is100%.
 2. The optical filter according to claim 1, wherein the opticalfilter further satisfies a requirement ΔT_(S) ^(0/40) ₆₅₀₋₁₂₀₀≤1%. 3.The optical filter according to claim 1, wherein the optical filterfurther satisfies a requirement ΔT_(S) ^(0/40) ₃₈₀₋₁₂₀₀≤1.5%.
 4. Theoptical filter according to claim 1, wherein the optical filter furthersatisfies requirements ΔT_(S) ^(0/50) ₃₈₀₋₅₃₀≤4%, ΔT_(S) ^(0/50)₄₅₀₋₆₅₀≤4%, ΔT_(S) ^(0/50) ₅₃₀₋₇₅₀≤4%, ΔT_(S) ^(0/50) ₆₅₀₋₁₂₀₀≤1.5%, andΔT_(S) ^(0/50) ₃₈₀₋₁₂₀₀≤2%.
 5. The optical filter according to claim 1,wherein the optical filter further satisfies requirements ΔT_(S) ^(0/60)₃₈₀₋₅₃₀≤4.5%, ΔT_(S) ^(0/60) ₄₅₀₋₆₅₀≤4.5%, ΔT_(S) ^(0/60) ₅₃₀₋₇₅₀≤4.5%,ΔT_(S) ^(0/60) ₆₅₀₋₁₂₀₀≤1.5%, and ΔT_(S) ^(0/60) ₃₈₀₋₁₂₀₀≤2.5%.
 6. Theoptical filter according to claim 1, wherein the optical filter furthersatisfies requirements ΔT_(S) ^(0/65) ₃₈₀₋₅₃₀≤5%, ΔT_(S) ^(0/65)₄₅₀₋₆₅₀≤5%, ΔT_(S) ^(0/65) ₅₃₀₋₇₅₀≤5%, ΔT_(S) ^(0/65) ₆₅₀₋₁₂₀₀≤1.5%, andΔT_(S) ^(0/65) ₃₈₀₋₁₂₀₀≤3%.
 7. The optical filter according to claim 1,wherein the optical filter further satisfies requirements ΔT_(S)^(30/40) ₃₈₀₋₅₃₀≤3%, ΔT_(S) ^(30/40) ₄₅₀₋₆₅₀≤3%, ΔT_(S) ^(30/40)₅₃₀₋₇₅₀≤3%, ΔT_(S) ^(30/40) ₆₅₀₋₁₂₀₀≤1%, and ΔT_(S) ^(30/40)₃₈₀₋₁₂₀₀≤1.5%.
 8. The optical filter according to claim 1, wherein theoptical filter further satisfies requirements ΔT_(S) ^(30/50)₃₈₀₋₅₃₀≤3%, ΔT_(S) ^(30/50) ₄₅₀₋₆₅₀≤3%, ΔT_(S) ^(30/50) ₅₃₀₋₇₅₀≤3%,ΔT_(S) ^(30/50) ₆₅₀₋₁₂₀₀≤1%, and ΔT_(S) ^(30/50) ₃₈₀₋₁₂₀₀≤1.5%.
 9. Theoptical filter according to claim 1, wherein the optical filter furthersatisfies requirements ΔT_(S) ^(30/60) ₃₈₀₋₅₃₀≤4%, ΔT_(S) ^(30/60)₄₅₀₋₆₅₀≤4%, ΔT_(S) ^(30/60) ₅₃₀₋₇₅₀≤4%, ΔT_(S) ^(30/60) ₆₅₀₋₁₂₀₀≤1.5%,and ΔT_(S) ^(30/60) ₃₈₀₋₁₂₀₀≤2%.
 10. The optical filter according toclaim 1, wherein the optical filter further satisfies requirementsΔT_(S) ^(30/65) ₃₈₀₋₅₃₀≤4.5%, ΔT_(S) ^(30/65) ₄₅₀₋₆₅₀≤4.5%, ΔT_(S)^(30/65) ₅₃₀₋₇₅₀≤4.5%, ΔT_(S) ^(30/65) ₆₅₀₋₁₂₀₀≤1.5%, and ΔT_(S)^(30/65) ₃₈₀₋₁₂₀₀≤2.5%.
 11. The optical filter according to claim 1,wherein the light absorber is formed by a phosphonic acid and copperion.
 12. The optical filter according to claim 11, wherein thephosphonic acid comprises a first phosphonic acid having an aryl group.13. The optical filter according to claim 12, wherein the phosphonicacid further comprises a second phosphonic acid having an alkyl group.14. An imaging apparatus comprising: a lens system; an imaging devicethat receives light having been transmitted through the lens system; andthe optical filter according to claim 1 that is disposed ahead of theimaging device.
 15. The imaging apparatus according to claim 14 furthercomprising a color filter that is disposed ahead of the imaging deviceand is a filter of three colors, R (red), G (green), and B (blue),wherein the optical filter is disposed ahead of the color filter.